1650 gas engine tuning help

jasinpa

Member
quick run down , bought a 1650 gas didnt run , found it had burnt valve , cyls. look good so rebuilt the head put back on got 175 lbs . compression in all cyls , holley distributor was worn out & do to lack of parts for them replaced with a new delco style ,no vaccum adv., from Korves , replaced plugs , wires , set timing to TDC @ idle / runs close to 22 deg. @ 2000 RPM's. , got her all running but cant get idle down to 500 like it should be , lowest it will go with out shutting off is 800 , so i rebuilt carb , which is in good condition , soaked in new carb. cleaner for a day , made sure all passages where open with a small wire & air gun , installed new kit,but couldn't get main jet/ suction tube out didnt want to break it & kit dont come with it anyway so left it in. anyway installed back on engine runs better but still cant get idle down lower then 800 , also if you run it wide open & pull it back to idle it will sometimes shut off & if it dont it will stumble to remain idling for a min. the smooth out , but other wise runs great. I have tried moving timing some , tried moving carb. adjustments , but cant fix this problem. also it idles the best with carb. idle screw turn in all the way , id think it should shut down at the point wouldn't it ? not that it should matter but i went throw govenor & reset likage to spec. works great as it should ,but dont really have anything to do with idle since its held in the off postion at that point. what do you guys think the next step to try should be , is it in the carb.? maybe the new distributor is causing this do to the lack of vac. advance ? the 1600 didnt have vac. adv. & had no problem , but ive tried more advance didnt help. sorry for being long winded but to get any help w/ this i need to be as detained as possible , ive got lots of engine experience but this one got me .
 
First check the idling speed indication is correct.

Problem is highlighted as idling with the carb idling screw full in. Your problem most likely is based around that.

Float chamber level comes to mind as well as Chuck?s suggestion. A leak at the butterfly rod might be another.

Question is whether it is rich or lean at idle? Until you know that you are on to a loser, as far as rectification is concerned.
 
i will check out manifold for leak , i did replace the exhaust man. with a new one so all gaskets are new there , thanks
 
before you install the manifolds put them together only snug not tight, then bolt them to the head snugly to align them then tighten them up.
 
yep thats how i bolted manifold up so it was in line with head , & yes i plugged the vac. hole . tonight i pressurized the intake manifold with some air & spayed soapy water to see if it leaked anywhere & it dont , even @50 PSI which is more then high vac. would ever be. its looking like carb. trouble more & more but what would be wrong i wouldnt have a clue , its in great shape & there not cheap to buy used or rebuilt and then if the problem is still there it was a waist of $400 bucks. anyone els have some ideas to throw at me ? im not giving up on this one just scratching my head at the moment.
 
Do you have a vacuum gauge? They are a very good for finding problems! Send me an e-mail and I will send you a list on how to read the gauge readings. J.
 
does sound like a lean condition...if it's a marvel carb they are so simple it's hard to believe they can be so problematic but they can...could be it. Could be leaking/sucking air around the needles. Mine was, had a guy who used to work on them rebuild mine after I did...been good for years now.

First 2 things I'd check is the fuel delivery system and the gaskets from carb to head. Crap gets stuck all over in the fuel delivery and I've had carbs not properly sealed doing exactly what you describe. Easy way to find any leakage is using some starting fluid. Spray it near connection and if she picks up, that the spot.

People fool around with carbs...off/on, off/on wears out the bolts/holes maybe breaking some.

My 1850 had a problem that did a similar thing...New cap and wires weren't happy with each other, coil wire would pop off just enough so it wasn't noticeable unless you were looking for it. Fixed it on well and never another problem.
 

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