Carb work VS. modern gas

[Freebird]

I recently heard from one of our California members that he had been having some performance problems with his first gen Venture. He said that he finally got it resolved by a very good mechanic and some carb work. Turns out that it was caused by the gas that was being sold in his part of the country and I think that it is a very valid point. I asked him to let me know what was done and here is the answer to my question. I find it very interesting and it makes a lot of sense to me. I think it could also apply to the second gen Venture.

 

Here is the response:

 

Hi Don, good evening. I'll be as brief as I can, although Mary tells me it just isn't in my genetic make-up! My bike had just had a total engine rebuild, so should have run well, but not so. I kept fiddling with it, and it sort of ran okay, and was a rocket on the freeway. I went to this engine guy, Larry Holt, who has done two V-8's for me...I know how, but I'm 62 now, and someone else can do it for me. I told him I thought I had ignition trouble, and he said no way, not if I can do 80 on the hiway. And if Mary and I wanted to just putt around looking at the sights, the bike would run on it's own at 3000 rpm. I couldn't shut it off with the throttle return twist. Larry's solution was that there was a lean running fault because of the rotten gas we get here, and I'd messed up the carb sync trying to get it to idle as well as it did. We reamed the pilot (idle) jets in all four carbs from 16 thou to 18 thou, and reset the sync. An absolute miracle. Runs like a dream, with a ton of throttle response. The bottom line seems to be: the carbs were designed and built before the garbage gas here in California, and with all the added alcohol, they now run lean. Just for laughs, I put in some 110 octane aviation gas, and oh my! What a ride! Hope this helps someone, somewhere.....Best regards, Mike

[Redneck]

I can't believe a lean idle mixture would cause the idle speed to rise much. My guess is the carbs were way out of sync. With the fuel formulas these days there is no doubt that the calibration of the carbs are not optimal. the factory sets the carbs to work at a wide variety of conditions and tuning for your local environmental conditions and fuel formula no doubt will yield a significant gain in driveability characteristics.

[Yammer Dan]

Color-Tuning Carbs should be the way to go then???

[Condor]

I can't believe a lean idle mixture would cause the idle speed to rise much. My guess is the carbs were way out of sync..

 

I agree with you Mike. I burn that Ca fuel and have no problems what so ever. While resurecting 83#2 I found that the idle had to be backed off a ton after syncing the carbs. My guess would be that punching out the jets didn't do a thing other than clean them out and cause the motor to run richer and maybe reduce the mpg.

[Stoutman]

I know it is counter-intuitive that a lean condition can raise the idle, but let me share an experience. I had to do a bunch of remodeling on an old house, so I bought a used dump truck from a state auction. When I drove the thing home it was almost racing the engine at idle. Whenever I stopped I was afraid the thing would blow up it idled so high. So I stopped in a parking lot and opened the hood. When I took off the air cleaner I noticed that the studs holding the carb down had no nuts on them, and the accelerator spring caused the carb to tilt up off the manifold, bypassing the butterfly valve in the carb and letting air in. I happened to be by a hardware store so I walked over and bought a couple of nuts and threaded them down hand tight. When I started the truck up again it ran fine. All that extra air essentially leaned out the mixture a bunch. It was not the lean condition that caused the idle to increase as much as it was the extra air. What fuel there was heated a much larger volume of air, causing an increase in the idle speed. So your intuition is correct, but when you factor in why it is lean (extra air volume) you still get the same result.

I'm not dissagreeing that this guys carbs were out and reaming the jets really didn't help. I don't know all the variables on his bike. I'm just saying a lean mixture can make the idle go way up depending on why there is a lean condition.

[Condor]

I know it is counter-intuitive that a lean condition can raise the idle, but let me share an experience. .

 

I think the thing your missing here is that the mechanic blamed the CA ethanol fuel for the cause of the high RPM condition, and that by richening the mixture the problem disappeared. I think it was something else that caused the condition, and by messing with the carbs it was corrected. CA fuel will not cause an engine to run lean. Maybe get less gas milage because it's less volatile, but lean.... nope..... MOF when I left for Ft Collins the first tank was CARB fuel and it only got a couple of miles less per gallon than afterwards when I started filling up with non-ethanol fuel, and the bike ran great the whole trip.

[pegscraper]

I say that reaming the jets out, or basically richening the idle mixture, is just exactly what was causing the idle trouble. If the idle circuit is so daggone lean that the engine can't get enough gas to run on just the idle circuit, it will get it from somewhere. When you turn the idle speed screw in far enough trying to get it to keep running, it will start to pull gas from the main jets, in which case it won't idle at all, or at best it will be extremely rough. The solution is to richen the idle circuit so it can actually feed enough fuel for the engine to idle.

 

I've seen this many times before in cars, but hadn't yet seen it in a bike. The GM cars starting in the late '60s and all through the '70s were really bad for this, especially the ones using the Q-jet carb. It was an early first stab at emissions controls - lean out the idle circuit. But they went way off the deep end with that. These cars would idle rough, and there was no way to adjust the carb to smooth it out; no usual way, that is. If you looked down the top of the carb there was liquid gas dripping right off of the boosters. The idle circuit was so lean that it couldn't supply enough fuel for the engine to run, and it would pull fuel from the main circuit, the boosters. Turning the mixture screws out could not fix the problem, because the idle circuit was choked down elsewhere in the carb body. In fact, turning the mixture screws had almost no effect at all on the way the engine idled. The only way to fix the problem was to open up the idle circuit, and it was designed to be very difficult to modify. The idle jets weren't designed to be changed. The orifice that needs opened up is at the end of a long, thin tube in the main body. A drill bit about .039 and about 2 inches long is needed, and they are hard to find. Once the idle jets were drilled out, suddenly the engine ran smooth, gas no longer dripped off of the boosters at idle, and the mixture screws were responsive. It is this characteristic of the Q-jet that earned them such a bad reputation, and many people threw them out and replaced them with a Holley or something else that was tunable.

 

In my own experience with late '60s Cadillacs, before I fixed them, they would blow a pile of carbon out of the tailpipe every time they started up, and the exhaust at idle stunk so badly it would burn my eyes and drive me right out of an open garage. I used to keep cardboard behind the cars to keep the wall and floor clean. After fixing the idle circuit, they no longer blew carbon out when they started up, I no longer needed the cardboard, and I couldn't smell the exhaust at idle at all. Ironically, leaning out the idle circuit not only made the car idle like crap, it also made emissions worse, because they took it way too far. Richening the idle circuit back up to where it belonged made emissions better and the engine ran better too.

 

Mechanics who have been working on cars for a long, long time and have observed what happened to cars since the start of the emissions era know this kind of stuff.

 

Even with our current bikes, those who are really tuned in to the way the engine runs, know that when they richen the pilot jets, the engine will run smoother. It wasn't all that bad to start with, not like the cars I just described, and most folks won't notice enough roughness to complain about it. But they are on the borderline of it. Richening the idle circuit up where it belongs makes them run smoother.

 

Even my wife, who knows nothing about tuning an engine, suddenly noticed a difference in her bike one day. I had richened up the idle circuit a bit and removed the AIS crap. I didn't tell her that I had done anything at all. I just did it, out of principle more than anything, and then rode around the block to make sure it was good. Within a few days she asked me if I had done something to her bike. I asked why. She said it was running a lot better, and smoother. She said that she wouldn't have called it bad before at all, but something was definitely different. It took a few seconds for it to sink in with me, and then I started laughing. I wasn't familiar enough with her bike to notice a difference in the idle smoothness myself when I rode it, but she, without knowing that I had done anything to it at all, could tell something had happened for the better.

 

I like breathing clean air as much as the next guy, and I wouldn't want an engine to run too rich and make the exhaust dirtier than it needs to be. But leaning the engine out too much causes just as many problems, if not even more, than it solves.

[Condor]

I like breathing clean air as much as the next guy, and I wouldn't want an engine to run too rich and make the exhaust dirtier than it needs to be. But leaning the engine out too much causes just as many problems, if not even more, than it solves.

 

What you've said is spot on. And this relates to ethanol fuel.....how??

[gibvel]

I say that reaming the jets out, or basically richening the idle mixture, is just exactly what was causing the idle trouble. If the idle circuit is so daggone lean that the engine can't get enough gas to run on just the idle circuit, it will get it from somewhere. When you turn the idle speed screw in far enough trying to get it to keep running, it will start to pull gas from the main jets, in which case it won't idle at all, or at best it will be extremely rough. The solution is to richen the idle circuit so it can actually feed enough fuel for the engine to idle.

 

I've seen this many times before in cars, but hadn't yet seen it in a bike. The GM cars starting in the late '60s and all through the '70s were really bad for this, especially the ones using the Q-jet carb. It was an early first stab at emissions controls - lean out the idle circuit. But they went way off the deep end with that. These cars would idle rough, and there was no way to adjust the carb to smooth it out; no usual way, that is. If you looked down the top of the carb there was liquid gas dripping right off of the boosters. The idle circuit was so lean that it couldn't supply enough fuel for the engine to run, and it would pull fuel from the main circuit, the boosters. Turning the mixture screws out could not fix the problem, because the idle circuit was choked down elsewhere in the carb body. In fact, turning the mixture screws had almost no effect at all on the way the engine idled. The only way to fix the problem was to open up the idle circuit, and it was designed to be very difficult to modify. The idle jets weren't designed to be changed. The orifice that needs opened up is at the end of a long, thin tube in the main body. A drill bit about .039 and about 2 inches long is needed, and they are hard to find. Once the idle jets were drilled out, suddenly the engine ran smooth, gas no longer dripped off of the boosters at idle, and the mixture screws were responsive. It is this characteristic of the Q-jet that earned them such a bad reputation, and many people threw them out and replaced them with a Holley or something else that was tunable.

 

In my own experience with late '60s Cadillacs, before I fixed them, they would blow a pile of carbon out of the tailpipe every time they started up, and the exhaust at idle stunk so badly it would burn my eyes and drive me right out of an open garage. I used to keep cardboard behind the cars to keep the wall and floor clean. After fixing the idle circuit, they no longer blew carbon out when they started up, I no longer needed the cardboard, and I couldn't smell the exhaust at idle at all. Ironically, leaning out the idle circuit not only made the car idle like crap, it also made emissions worse, because they took it way too far. Richening the idle circuit back up to where it belonged made emissions better and the engine ran better too.

 

Mechanics who have been working on cars for a long, long time and have observed what happened to cars since the start of the emissions era know this kind of stuff.

 

Even with our current bikes, those who are really tuned in to the way the engine runs, know that when they richen the pilot jets, the engine will run smoother. It wasn't all that bad to start with, not like the cars I just described, and most folks won't notice enough roughness to complain about it. But they are on the borderline of it. Richening the idle circuit up where it belongs makes them run smoother.

 

Even my wife, who knows nothing about tuning an engine, suddenly noticed a difference in her bike one day. I had richened up the idle circuit a bit and removed the AIS crap. I didn't tell her that I had done anything at all. I just did it, out of principle more than anything, and then rode around the block to make sure it was good. Within a few days she asked me if I had done something to her bike. I asked why. She said it was running a lot better, and smoother. She said that she wouldn't have called it bad before at all, but something was definitely different. It took a few seconds for it to sink in with me, and then I started laughing. I wasn't familiar enough with her bike to notice a difference in the idle smoothness myself when I rode it, but she, without knowing that I had done anything to it at all, could tell something had happened for the better.

 

I like breathing clean air as much as the next guy, and I wouldn't want an engine to run too rich and make the exhaust dirtier than it needs to be. But leaning the engine out too much causes just as many problems, if not even more, than it solves.

 

Wanna come adjust my carbs?

[Freebird]

Well I'm just sort of thinking out loud here. Maybe the ethanol has nothing to do with it at all but I'm still not convinced. Most test show that the gas with ethanol produces poor fuel economy, that's just ONE of the reasons that ethanol is NOT a good solution to any oil shortages. It is not as volatile or something. So if you are really not getting enough actual energy producing fuel, but are still getting as much air as before, it just seems to me that it could indeed cause a lean condition and that maybe drilling the pilot jets out did indeed help with the problem.

 

I will be the first to admit though that carbs are not my specialty. In fact, come to think of it, I HAVE no specialty.

[pegscraper]

What you've said is spot on. And this relates to ethanol fuel.....how??

 

I look above and see where you agree with someone who said that a lean idle mixture had nothing to do with the problem. Then when I say that a lean idle mixture is the whole problem, you say I'm spot on. So what gives?

[FreezyRider]

I will be the first to admit though that carbs are not my specialty. In fact, come to think of it, I HAVE no specialty.

 

 

WRONG!!!!!

You run a slam-bang forum, Don. I'd say THAT is one of your specialties!!

[Condor]

I look above and see where you agree with someone who said that a lean idle mixture had nothing to do with the problem. Then when I say that a lean idle mixture is the whole problem, you say I'm spot on. So what gives?

 

 

After re-reading your post I'm going to retract the 'spot on' statement. I'm still going to ask the question. Why does Ethanol cause a lean air/fuel mix? Your response covered a lot of areas, some I agree with, and others I don't, but that's not important. The reason for my first post, and one that you never really addressed was; How does Ethanol cause a lean fuel/air mix. I'm always willing to learn something. Can you explain?

[Freebird]

Please see my previous post. Same amount of air, less volatile fuel with the ethanol mix. Could that not cause a lean condition? I'm not saying that it does, I'm asking sincerely.

[Yammer Dan]

I would think it would have to. I know the "New Gas" seems to go bad quicker also. And cause more of a mess.

[Condor]

Please see my previous post. Same amount of air, less volatile fuel with the ethanol mix. Could that not cause a lean condition? I'm not saying that it does, I'm asking sincerely.

 

Think about it this way Don. The air/fuel ratio will stay the same no matter what liquid flows thru the carbs at a given air velicity.. The difference between non-ethanol fuel and ethanol fuel is virtually nothing, as far as the ratio is concerned. The difference lies in how many BTU's are developed between the fuels. Less BTU's less power...less MPG. The mix of ethanol in the state of CA is 5.7% by volume. Sure it's going to reduce power output, but not by a bunch. And if it were 'crappy' gas every 1stGen in the state would be having the same problem. I don't see that. Common sense tells me that the diagnosis given by the mechanic ' Larry's solution was that there was a lean running fault because of the rotten gas we get here', and his fix is to punch out the jets, might have corrected a mechanical problem.... liked plugged up idle jets, rather than to correct a lean burn situation because of 5.7% ethanol in our fuel. Sorry for the long response.... it's catching....

[Condor]

I would think it would have to. I know the "New Gas" seems to go bad quicker also. And cause more of a mess.

 

ya gotta get out and ride more Dan......

[Thom]

i guess nobody here has run a straight alcohol motor before ,one of the 1st things you do is ream out the jets , the biggest problem alcohol motors is that they run to lean . alcohol fires to fast so the cylinder runs dry before the piston gets to the bottom of the stroke . alcohol has a fast burn time and a small expansion witch is good for a short stroke engine , gas has a long burn time and long and large expansion , witch is good for long stroke engines [ us ] it is why small motor do good in Ca. but a 440 can't get out of it own way , ok i don't teach school no more , it been 35 years .:bang head::rotfl:

[Jrichard]

when i run any ethonal based fuel,I always add the suggested SEAFOAM-1 oz. per X amount of gal.---------to the full fill-up---- my 2 sheckles worth of info!! non-etholal will always preform better-----------