Idle screwy after highway miles

[Ross72SIII]

Hey all,

Decided to drive my 109 from Burlington VT to Cape Cod (300-350 miles...so far). Im happy to report we are both doing well. The only issue Im having is that after all those highway miles the truck seems to want to run away on me. The RPMs will increase moderately, then take a second or two to return to normal idle speed, when I pull up to a stop light and put the clutch in. Happens a lot more when the engine is very hot. If I slowly downshift and very carefully come to a stop this usually does not happen. When its above idle at a stop I can tap the accelerator very lightly, the engine with grumble very slightly, then it will return to proper idle.

Ive adjusted the idle screw a little (6 month old weber) both ways with no affect (so I put it back to original settings from the its tune up last week). Ive also oiled all the connections in the entire throttle linkage system from the petal to the carb just in case it was sticking somewhere. No luck there.

Any ideas?

As a side note, the 2.25 (gas) seems to have seriously benefited from some time on the highway and some marvel mystery in the gas tank. Running great with a little more power after cleaning it out on the highway.

Ross

[knac1234]

Ross,

I can only share my limited experience with my 72 SIII 88. Idle increased due to a faulty brake servo. Did the plug fall out or come loose on the booster? My booster needed replacement, which cured the problem.

Probably not the answer, but a quick check might tell you!

BTW....how fast were you averaging on the highway.....just curious!

Julian

[crankin]

throttle return spring old or loose? When it revs up like that instead of pushing down on the peddle....put your foot under and push it up. What does it do?

I would agree with the booster thought. Also, is the choke is opening fully? You might also, clean out the fuel bowl and blow out the jets.

[Billy5]

I had the same issue. I also have a weber on my 88. What I found was I needed to snug up the nut on the back side of the carb where the linkage connects to the carb. If this is loose, it won't allow the throttle to return fully. I find I have to do it every couple months. You will see it when you look, it is 7/16 i believe. Hope this helps.

[Ross72SIII]

Thank you all for the tips.

I very quickly isolated the issue to the carb yesterday when the truck lost idle, started smoking and died in Marblehead, MA (tiny streets, angry drivers) 4th of July traffic. Some people were very upset with me. It was great.

When I got it back to life it was extremely rough and smokey. I Made it half way to my fathers garage and then unfortunately had to call the tow truck as it totally quit on me. I took the air filter hose off and immediately noticed fuel DUMPING in with only half throttle. So Im guessing either a stuck float or im all clogged up. There was a ton of crap in the sediment bowl after the trip. I do have a paper filter between the bowl and the carb, but something might have snuck by and clogged me up.

Julian-The speedo cable broke, so I was flying blind. But no one gave me the finger on the way down so I guess I was keeping up alright. My guess...60mph on the highway. The hills in VT really slow things down, but once I hit Southern NH and MA I was cruising.

The scary thing was that I was actually passing people...on an incline no less!

Ross

[Ross72SIII]

Took the carb apart, completely apart, in the solvent tank. No sign of issues there. Ordered a new fuel pump from our hosts. After talking with Les it may be that the pump is on its way out and sending a little too much fuel to the carb. Well see.

On a side note, the pump came right off. All the fuel line fittings came right off too. This is too good to be true. On account of everything coming apart and going well tonight I think Im doomed tomorrow.