Unusual Engine Problem

[Celica_73]

OK Quick run down. Recently rebuilt engine 3000km ago to a 2tG/3t hybrid. Got the engine running fine purred away from day 1 until I rebuild the Carbies due to leaking accelerator pump 1000km ago. Although the car was great straight after the carby rebuild 3 days later (also new tank of petrol) it has developed a weird surging at low throttle position and seems to have a decaying idle on 3 cylinders and continue to run on 3 until 2000 RPM but if you then lower the revs while driving along on 4 cylinders again to 1500 and accelerate maintains to runs on 4 cylinders. One other Strange thing thats has occurred since first day of fire the engine after engine rebuild is the revs do not drop quick enough, it hold rev for a while before dropping.

OK now for the list of things I've replace and checked.

Small venturies all tight
Timing
Changed Spark plugs
Ohm metered Leads
Cleaned Dizzy Cap
Check all nut hold the Carbies to manifold
Replaced air cleaners (need to anyway)
Rebalanced the carbies (they were the same as i left them after the rebuild)
Compression test 1:175 2:172 3:168 4:174
Check Cam timing
Check Valve Clearances
Looked or Vaccum leaks yet to Find one.
Search the Forums and the web of other cases.

Note jetting in carbies is stock. Old style Solex (Not external adjust on float)
Check float levels on balancing and adjust to 2tg specs) All tuning has been to suit a stock 2tg minus the cams dialed in to spec.

Cheer and ideas would be helpful. I'd take it someone to look at but due to my location no one knows how to tune twin solex carby engines around here. I don't know if jetting is to blame although it was running smooth before. Since the surge started I have emptied the tank and refuel with a different fuel still same problem

Jason

[mike1980ra40]

I had a similar problem with my 18RG rebuild, a small part of it will be new rebuild teething
problems. what you've described sounds like a carby problem like I had. have you checked
for airflow thru the pots... if not, start up the engine and while its idling ( with air cleaners
off ) and block off the intakes one at a time and see if the rpm drops or idling is yet more
lumpy. if you've blocked off one intake and theres no change in the engines rpm or running
then that will be where the problem is. best thing you could do is get an airflow meter,
not a lot of auto stores will have those, performance stores probably a better bet.

another thing you could do is grab a length of garden hose (old skool this is but works )
and listen to the sucking of each intake, you'll be able to hear which carb has the problem
and which pot.

[Celica_73]

Ok I've found the proble!

It was the idle/pilot jet on cylinder 3 partly block. I tried the hand over each throat but each only made the idle lump. Next i removed leads one at a time to locate a cylinder and made sure it was repeat able. And after some reading on the web and post on the forum one by i found the main jet doesn't come into play when throttle at less then 20% about cursing speed and idle. Anyway problem Fix.

Cheers mike1980ra40 for the input.

Jason

[mike1980ra40]

no worries, good to see you got it sorted
cheers.