vanguard missfire after 2 barrel swap

fisherj21

i have a 18hp vanguard with governor removed, rev kit, cam advanced 1 tooth and it also has 16hp heads for more compression, engine ran real good, i just installed a 2 barrel carb and intake and now cyl 1 is missfiring at lower rpm, cyl 1 is getting good spark, and it has good compression, for sh*ts and giggles i swapped plugs and it did the same thing and i also swapped out a known good coil and it still has the same problem, i have pulled carb apart and cleaned twice and its still the same problem, for sh*ts and giggles again i used a not lit propane torch and fead a little propane in the carb for cyl 1 and the missfire goes away and runs fine, so i a pretty sure there is a problem with the carb, i have removed all the jets in the bottom of carb and blew air through all the passages, am i doing something wrong with cleaning this carb ? what else should i look for ? thanks in advance

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	carb2.jpg (98.6 KB, 0 views)

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sho305

I would check idle circuit for that cylinder is my guess, one spec of crud in the right spot will do it. Also look for air leak in gaskets/etc. they can show up more under vacuum of low throttle and go away when you gas on it.

beater cart

When you clean the carb are you pulling it all the way down removing the idel adjustment screws and such.

chevydmax6

Have u checked the throttle plates are both closing all the way check them with a light from one side
Or like everyone else make sure the idle circuit is cleaned
I see u have the idle ajustments on top richen up the cylinder that is misfiring
U maybe one to find a new carb that u can put an adjustable needle in for the main jet

fisherj21

i pulled out the idle jets like was recommended, and cleaned the ports out and put back together, i was able to get the cart to idle pretty smooth now, its 100 times better then what it was, thanks for the help, i did not know tose idle adjustment screws were able to come out

fisherj21

i finally was able to get my cart put back together and now i have a bad stumble in mid range rpm if i hit the gas to the floor, i also have a stumble if i hit the gas to floor on take off, i noticed that the stumble is not as bad when i drive the cart with the air filter removed, and the air filter is new and stock type, what an i do to fix this, thanks in advance

beater cart

Play with the idle adjustment screws try pulling them both out 1/2 a turn see how it preforms if not any better try 1/2 turn in from original settings see witch way makes it run better.

fisherj21

i messed around with the idle screws, and it runs the best about 1/4 turn in from the stock setting, the engine will rev up decent with the air filter off but as soon as you put the filter back on it has a stumble right off the line and then then a stumble if you are going part throttle and then smash the gas it will stumble a bit and then go, i had a 18hp single barrel carb on this engine before and i think the single barrel had more power, i checked the plugs and they are brownish and i reset the valves which helped a little, is there any jets i need to drill out to get rid of the stumble?

sho305

It can be strange to figure out. Some carbs you take the airfilter off and its leaner because it was restricting it. But other things you do that and its richer because the air is funneled into the carb better by the airbox housing than having nothing on it. Keep messing with it, should run better once its right.

Alex Faught

Put a large mc carb on it. Jetting is a cinch as well as tuning.