Idle problem with 65 Riv.

[Guest JDagg]

I am having a problem with my 65 Riv., the motor was recently totally rebuilt at a performance machine shop. After driving a few weeks, I detected some problems which I believed were related to the carb. since it had not been touched. It was hesitating or lurching when going up hill, but appeared to be ok on the straight and level, so I had my carb. professionally rebuilt. After overhaul they ran it and sent me a video, so I believe that its good. I drove it to a garage to have it tuned up as was suggested by the carb. people. That was a week ago and now it has all gone down the tubes.

At first the mechanic attempted to adjust the carb but also adjusted the timing as well. When they finished I attempted to drive home but could not even get out of their parking lot. Took it back in and the trouble shooting began.

Next they had trouble just keeping it running, backfired and blew fuel out the exhaust, A fuel flow regulating device was put in line between the filter and carb. and turned down to 3 psi at the advise of the Carb. overhaul people (new filter by the way) No backfiring now, and sounds fine when the engine is throttled up but still appears to be blowing fuel out the exhaust, (and it idles rough). They switched out the distributor with a new one, still no difference. They now think the front two cylinders are what is causing the problem and believe its tied to a cam issue. The vacumm gauge is indicating a rapid flutter on either side of 14 inches. All new hoses and components. On a side note there is only one metal gasket on the carb. though and I thought there were supposed to be more.

Sorry for rambling but I am at wits end. Had the car since 1970 and am the second owner.<!-- google_ad_section_end -->

[Jim Cannon]

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On a side note there is only one metal gasket on the carb. though and I thought there were supposed to be more.

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There should be one stainless steel metal plate touching the base of the carb and one composite gasket between this plate and the intake manifold. You can sandwich the metal plate between two composite gaskets, if you want (if you are concerned about good vacuum seal between the carb base and the metal plate) but they originally came with no gasket between the plate and the carb.

If you have not done one yet, do a compression test on all 8 cylinders and compare numbers.

Did you add GM Break-in Additive (ZDDP) to the motor oil after the rebuild?

Is the performance machine shop the ones looking at the engine? It's their work, they need to stand behind it.</snip></snip>

[Guest JDagg]

Different outfit doing the work, but machine shop has been in contact with them. I don't have the numbers handy, but recall that all cylinders had excellent compressions.

Also did leak test around base of carb. and no leaks. Don't remember the break in oil, but a high zinc content oil was used. I have less than 200 miles on it since rebuild.

[Jim Cannon]

High zinc content is good for driving once it is broken in, but you need even more in the first oil used after rebuilt.

If you have good compression numbers now (not immediately after the rebuild, but now when it runs so poorly) then you don't have a cam problem like the mechanic is guessing.

Does this mechanic really know these old cars? They are different from modern iron.

It sounds like to me the wires going from the distributor out to each spark plug are on in the wrong order. It is easy to accidentally reverse a couple.

Is the ignition timing being done exactly per the shop manual? A lot of mechanics have the attitude "I know better" and they do what they want (what works for their Chevy that they work on all the time).

[Guest JDagg]

Thanks Jim, To tell the truth, they really don't know the old cars, and its hard to tell them anything. Don't get me wrong they are great mechanics and super good people, but they seem to be completely lost here. I know the very first thing the one mechanic did before he even tried to adjust the carb. was to take the distributor cap off. Didn't even hook up a gauge to it or anything. They do have my shop manual and seem to be starting to use it now. They are also calling anyone they can think of to get advise. I don't think the ignition wires were reversed but I guess it could have happened. Would the engine run ok at higher rpm if they were reversed? What about the fluctuation of the vacuum gauge? Also, it turns out I did have break in oil added, don't know what kind though. The high zinc oil was to be used for all subsequent changes. I will have them trace out each ignition wire today and see if that helps. Thanks again.

[Guest JDagg]

The mechanic just called and said that after he had changed out the AC spark plugs for Champions, it idled as it should. However, when he test drove it, acceleration on the straight and level was good, but once he incountered a hill, it began to falter and did not level out until he crested the hill. So under load there is still a problem. He then tried partially clamping off the fuel return line at the filter, and it improved somewhat but not all the way. Any ideas on this?

[RivNut]

That sounds like it could be a float level problem.

[Paul K.]

Thanks Jim, To tell the truth, they really don't know the old cars, and its hard to tell them anything. Don't get me wrong they are great mechanics and super good people, but they seem to be completely lost here. I know the very first thing the one mechanic did before he even tried to adjust the carb. was to take the distributor cap off. Didn't even hook up a gauge to it or anything.

They may know more than you think. From how it was running the mechanic may have thought it was an ignition problem so he removed the distributor cap looking for carbon tracks inside the cap between the terminals. This can cause backfiring rough idle, etc.

[Guest JDagg]

Actually when I brought it in it was running ok I came in to have the shop adjust the mixture on the newly rebuilt carb.,the backfiring didn't start till later. After having spent the past week with them, I think that these guys do know what they are doing. Newly rebuilt engine from a very reputable stand behind their product machine shop. Less than 200 miles on it.

Here is a brief in sequence summary. On first day came in to shop and they pulled distributor cap to check condition, then attempted to adjust fuel flow, (backfiring and blew fuel out tailpipes), checked for vacuum leaks (none), replaced the distributor along with new points and condenser (no change), new fuel filter ( no change), placed in line fuel restrictor (no change), rechecked timing (no more backfiring, but rough idle), rechecked wiring and correct run (no change), changed from AC spark plugs to Champion (had a change, no more rough idle) on test drive accelerated fine on level ground, sounded and ran great, but going up a hill under load car bucked and faltered, did this twice. Back on flat and level, all ok. Got back to shop and pulled a couple of plugs and they were black with fuel. Thought it might be a resistance wire problem, but checking at the coil, we have 12 volts continuously. The only thing left to us then is I believe the Carbureator. Is that the consensous of everyone or have we missed something?

[1965rivgs]

First things first..any mechanic who can competently service late model autos should have absolutely no problem servicing `60`s cars. If anything, working on pre-`70 cars is a breath of fresh air from the high tech engineering (accompanied by deep thinking) present on newer vehicles. I dont know your shop but the fuel restrictor scenario is a little strange....

If you have fouled two sets of plugs I would definitely scrutinize the carb. In spite of the fact you had it rebuilt the rebuilder may have not checked something very basic like jet sizes. Double check float levels, for gas filled float and proper jet sizes. If you have access to another carb you can swap out the carb to expedite matters. Try to minimize running time with a carb which is overfueling the motor. It is possible to ruin a fresh rebuild rather quickly this way. Maybe that is what took out the engine in the first place. Good luck

Tom Mooney

[carbking]

You have either too much fuel or not enough spark. Odds are about 9 to 1 in favor of the issue being spark. If you have this much fuel, its running down past the rings into the crankcase (check the oil for the smell of fuel on the dipstick); AND you would be unable to see the rear bumper of the car when the engine is running for the black smoke.

A few spark issues I have seen in the past:

(1) over-restored (painted ) engine compartment provided no ground to engine from battery

(2) BOTH resistor wires AND resistor plugs used (severely limiting spark)

(3) electronic ignition module in distributor that worked sporatically

(4) replacement coil with incorrect inductive reactance to work with condensor

And before anyone thinks this, I was not the carburetor rebuilder.

It still could be the carb, but attaching a diagnostic oscilloscope to the ignition would prove/disprove the quality of ignition. I really doubt this is the problem, since you have not mentioned the car looking like a mosquite-fogger.

And the dial type $30. inline fuel regulators are extremely useful if you have a strong arm and a rabbit problem in your garden!

Fuel issues which might cause the problem with accelerating up a hill would include:

(1) partially clogged fuel sock (VERY common with modern fuel and a vehicle that sits without being driven)

(2) partially clogged fuel tank vent

(3) partially clogged fuel filter

(3) one of the dial type $30. inline fuel regulators

Keep posting. These cars are not rocket science. Good compression, correct amount of fuel, good spark all at the proper time, and the engine will run.

Jon.

Edited September 27, 2012 by carbking (see edit history)

[1965rivgs]

Dont rule out a combo of problems...at low RPM there could be a problem with overfueling (high float level, gass filled float) and at high load, hi RPM a problem with volume delivery as mentioned. You are fouling plugs, that is for sure. Check the ignition on a scope, as mentioned. Be sure the coil polarity is correct and the wires have not be reversed at the coil. This will produce weak spark. If nothing move on to the fuel system. Concentrate on too much fuel as we are sure from the spark plugs (they are your ally in the cylinder) you are overfueling (if ignition checks OK). Correct one problem at a time (starting with the most obvious/definitive) and if you are dealing with a combination of problems they will unravel. Good luck!

Tom

[Jim Cannon]

Actually when I brought it in it was running ok I came in to have the shop adjust the mixture on the newly rebuilt carb.,the backfiring didn't start till later. After having spent the past week with them, I think that these guys do know what they are doing. Newly rebuilt engine from a very reputable stand behind their product machine shop. Less than 200 miles on it.

Here is a brief in sequence summary. On first day came in to shop and they pulled distributor cap to check condition, then attempted to adjust fuel flow, (backfiring and blew fuel out tailpipes), checked for vacuum leaks (none), replaced the distributor along with new points and condenser (no change), new fuel filter ( no change), placed in line fuel restrictor (no change), rechecked timing (no more backfiring, but rough idle), rechecked wiring and correct run (no change), changed from AC spark plugs to Champion (had a change, no more rough idle) on test drive accelerated fine on level ground, sounded and ran great, but going up a hill under load car bucked and faltered, did this twice. Back on flat and level, all ok. Got back to shop and pulled a couple of plugs and they were black with fuel. Thought it might be a resistance wire problem, but checking at the coil, we have 12 volts continuously. The only thing left to us then is I believe the Carbureator. Is that the consensous of everyone or have we missed something?

You should not have "12 volts continuously" at the coil when the engine is running. You should have about 8 or 9 volts, due to the resistor wire in the harness. It is only supposed to be bypassed when starting (cranking). If you still have stock points and coil, they are going to burn up. Any signs of anyone running a new power feed wire to the coil? (where they have bypassed the resistor wire in the harness)?

Try measuring the resistance across the coil terminals with a good ohmmeter (remove one wire so that you only measure resistance through the coil windings). It should be about 1.5 ohms, more or less (engine not running, of course) if it is stock. If it is more like 3 ohms, then you should have full 12 volts to it (but that is not stock coil).

Make sure you have vacuum advance diaphragm connect to the proper vacuum source on the engine or carb. Use a vacuum gauge to see how much vacuum you have at idle and at slightly higher RPM. Confirm the vacuum diaphragm on the distributor is good. Make sure it will hold a vacuum. Sometimes they split with heat/time.

Make sure they set the initial ignition timing at 2.5 deg BTDC at a low RPM (around 400 is good -- so that the mechanical advance is not kicking in) without the vacuum line connected, then connect it and see RPM increase. Do not assume that if RPM goes up the vacuum diaphragm is good. Test it separately. Note to '63 Riv owners, this is different timing spec -- use 12 degrees BTDC for your '63.

Make sure all of the carb secondary mechanism is moving freely. Make sure the choke mechanism that is designed to lock out the secondaries is not getting in the way when the engine is fully warmed and the choke is fully open. A small misadjustment on that one linkage will result in you not having your 2nd pair of throttle plates open. The engine should run OK in this condition, you are just running a 2-bbl carb, that's all (no "get up and go").

Make sure the flapper above the secondaries inside the carb is moving freely. Bucking and falter on a hill sounds like the secondary throttle plates are opening but the fuel that is supposed to be flowing to go with the added air is not being delivered, or too much is being delivered. I would check all jets and passages in the secondary fuel delivery system for correct jets, missing jets(!) and possible trash plugging something up. I know you just had it rebuilt, but "stuff happens". Do you have anyone near you that you can borrow a known good carb from?

Did you try sandwiching your metal carb-to-intake manifold gasket between two fiber gaskets? That eliminates vacuum leak between stainless steel plate and carb base. It's not quite stock but removes one more uncertainty. I have seen exhaust get sucked into the carb from the carb heater passage milled into the top of the intake manifold. That can cause some of the symptoms you describe.

A stock mechanical fuel pump (I assume that is what you have) does not need a pressure reducer in line to the stock carb. That is BS. These engines were built to work as a system. If you have an electric fuel pump, well then you create your own problems and you have to fix them.

I always use AC plugs on these engines; that's what they were designed for. If switching to Champions helped, it's only because the AC plugs were fouled. Any new plug would have performed better.

How did they "checked for vacuum leaks (none)"?

What kind of ignition wires (specifically) do you have and how old are they?

Can you post the compression test numbers for each cylinder? Capture and report 3 readings in a row from each cylinder while cranking. All plugs should be out and the throttle should be blocked fully open when cranking. Do not use one of those handy push-button starter cranker things that connect to the starter solenoid with alligator clips; they will fry the wires in a '65 Riv. Use the ignition key/switch in the car to crank.

[Guest JDagg]

Thanks for all the replies. I have been out of town this past week and have not had a chance to respond. I am going over to the shop today to see what they have found out.

But at last report, with everything back to stock, (no fuel regulator) the car accelerates nicely, idles smoothly, does not backfire or blow fuel out the exhaust, but when it goes up a hill, any hill, it hesitates as if its not getting enough fuel. Once you let off the pedal, it takes a couple of seconds for it to regain enough fuel? to continue up the climb. At no other time does the car do this. On the straight away from a standing start with heavy acceleration there is no hesitation what so ever (they tell me). ???????

[Guest JDagg]

Here is the latest. With the return fuel line from the filter clamped off, the engine performs perfectly. Only problem of course is the possibility of over fueling the carb. and of course excessive fuel consumption. Question; is the pump which is currently on it, the correct pump. They changed it out with another new one of the same type, supplied by the local parts place, but is it really correct. Is there a higher volume pump available that will fit this engine, such as the one for the 425?

[RivNut]

The return line only came on a/c equipped cars. It was there to prevent vapor lock when driving with the air on in extremely hot conditions. If the car runs better without it and you don't experience any vapor lock, I see no reason to not leave it blocked off. If you find that you don't need the return line, You could get a filter that has only one outlet, and block the return line off farther down in the engine compartment so it wouldn't be out there just "hanin' around." Some of the tech advisors might know of a different reason for leaving it connected and/or know what the problem is and how to correct it w/o removing it.

Ed

[Guest JDagg]

Thanks, that kind of confirms what I'm thinking as well. But the question in the back of my mind is why is it behaving this way now? Are there differences in the construction of the fule fileters now vs. back when? I am going to the store to pick up the single line filter and have them try it out. Of course now comes the hard part, what is my bill going to be like, I mean in the shop for 3 weeks now, ouch. Thanks again.

[Jim Cannon]

The shop might have connected the filter up to the carb wrong, or it may not be the correct fuel filter. The center port should go to the carb. The vent port on the outer edge on this filter is supposed to have a small orifice in it that restricts the volume of liquid fuel going out the return line, thus forcing more fuel into the carb. If you reversed those, you would starve the carb for fuel.

What fuel filter brand and part number did you put on the car with the return line? I use Wix 33032 or NAPA 3032.

There is no problem with running without a fuel return line, except (as Ed notes) with A/C on in very hot weather, when you are not moving too fast (very high temperatures under the hood).

[Guest JDagg]

Same part numbers. I picked up the single line filter and dropped it off at the garage and hopefully they will have it up and going by this evening. I think we are going to call it good enough, but still wonder what the heck is going on. The car has been apart, from stem to stern trying to get to the bottom of this. They even took the fuel tank and sending unit back out again and blew all the lines out. New hoses, everything new, but still have the same problem. Thanks.

[1965rivgs]

It may be possible blocking the return line is enabling a weak fuel pump (or supply problem) to increase output to the point it is barely supplying enough fuel to keep the float bowl level adequate. Keep in mind there could be a problem/starvation on the supply side of the pump. The shop can troubleshoot a supply problem by temporarily setting up a fuel supply (gas can) and line directly to the fuel pump bypassing the tank and lines. Have the shop put an inline fuel pressure gauge on it at the carb and road test or just have them put another fuel pump on it (warranty?) if the supply side checks OK. Blocking off the return line is just a Band-Aid for an underlying problem which sounds like it is likely at some point to leave you stranded. Good luck!

Tom Mooney

[carbking]

Your initial post sounded like too much fuel, now it seems you have insufficient fuel.

One issue that can cause both is a clogged fuel tank vent. The vent is necessary to allow fuel to flow from the tank; and also can relieve excess pressure caused by heat. I do not know where the vent is located on your vehicle. Some of the 1960's vehicles were vented through the fuel cap. Changing to an unvented cap would create the problems you have experienced.

Often, vent issues will seem to be irregular or intermittant; however, they will generally follow a period of high fuel useage (the hill) or low fuel useage AND idle conditions. They can also be a function of temperature.

A return line, if properly installed, is NOT going to cause these issues. Today, return lines are routinely retrofitted to compensate for the pressure caused by the high volatility of todays fuel. As mentioned by another poster, the return line should have a restriction. Since a liquid will flow in the direction of the least resistance, the return line will see virtually no fuel if the carburetor fuel valves are in the open position.

Jon.

[Jim Cannon]

The vent on these cars is a dedicated line coming off the top of the tank with a rubber hose running down by the filler neck. Bugs do make nests there when these cars sit for a long time. Check that vent hose to make sure it is open.

The gas cap should unvented. The filler sits so low on these cars that gas will slosh out the filler neck when you accelerate if the gasket on the cap does not seal well or if you use a vented cap. (And at the high cost of gas today, you hate to have that happen!)

[carbking]

The vent on these cars is a dedicated line coming off the top of the tank with a rubber hose running down by the filler neck. Bugs do make nests there when these cars sit for a long time. Check that vent hose to make sure it is open.

The gas cap should unvented. The filler sits so low on these cars that gas will slosh out the filler neck when you accelerate if the gasket on the cap does not seal well or if you use a vented cap. (And at the high cost of gas today, you hate to have that happen!)

Jim - thanks for specifying the vent location. Different vehicles have it in different places.

Jon.

[Guest JDagg]

New vent line, new fuel lines, new sending unit, tank was thouroughly flushed, new non vented gas tank cap, still no clue. Am picking the car up this afternoon anyway, will let you know how it drives, two big hills between here and the garage.

[Guest JDagg]

Drives great. Fantastic acceleration, takes the biggest hills (although hard to find big hills in Oklahoma). When I drove this back in the 70's as a daily driver, never had a problem at all, I am wondering if the new fuel pickup sender unit might be the culprit??? New vent lines and supply lines, in addition to changing out the fuel pump twice. I don't think that vapor lock is going to be a problem for the type of driving I intend to do so this may never be an issue past this point. I want to thank all of you who contributed your ideas and expertise to this issue. Really appreciate what you have done to help. Thanks Jim

[Guest JDagg]

Thanks again guys for the help.