86 350x back fire then stalls, only when motor warms up

[Cujo909]

86 350x all stock besides UNi filter. No mods done to air box. Rebuilt carb yesterday. 42 slow and 138 main? Whatever stock is, the book says pilot 45, i know the main is right per book and sea level in michigan. rebuilt kit said 42 slow. Same problem no matter what slow jet I try. Pilot out 1 3/4 turn per Honda.Idols high as well. Runs fine till warm up Then backfires a lot and stalls. To me it says lean, but no mods and past experience with 350x that jetting should be fine. Checked valves fine. The history is it sat outside a lot till I bought it. Suggestions???

[Flyingw]

look on the bowl rim right under the hose nipple. If it says QA10A then you need that #45 slow jet. The #42 is too lean and you run the risk of burning up your motor letting it idle. I did the same thing with my 86 a few years back. They don't make a rebuild kit for the 86 carb so you have to reuse the #45 slow jet. When I did the initial engine start after rebuild, it idled about 2 minutes before I noticed my head pipe glowing red. Not good. The backfiring is telling you its too lean.

[6speedthumper]

Just for kicks, you did make sure that the mixture screw had a new o-ring on it, right? Figure I ask so all bases are covered.

[Cujo909]

6 speed thumper, yea installed o ring washer spring then pilot jet, 1. 3/4 turns out from light seat. Went back to 45 slow and now she only will run on half choke, I take choke off she dies. It's like it got worse after carb rebuild kit not better. 138 main is in it flyingw.

[Cujo909]

Just for kicks I had a 150 main in shop so I put that in. It runs no choke but I'm back to square one. Goes through gears fine. Let off throttle it backfires a lot then stalls. I've never seen a 4 stroke this picky, I'm thinking its got some other issues then the carb with jets.

[6speedthumper]

Have you made sure that all the intake tubes and manifold are okay? No splits, cracks, clamps tight? Have you changed the spark plug? Air filter clean?

[Cujo909]

Spark plug golden brown tip with black around outer threads. Not new. air cleaner is spotless.Now as far as exhaust leaks I feel one in the header and exhaust can go together. As far as the header itself i feel nothing being pushed out, is there a better way to test for leak on the header part? Thanks for the checklist so fair, I'm trying to narrow it down.

[bparker525]

not too experienced with 3 wheelers but well experienced with small motors on dirtbikes and fourwheelers and it sounds like your running lean try richening it a little bit to have a
high flow air filter with a jet smaller than stock does not make a good combonation you should at least have a stock jet maybe even a size up if richening the mixture doesnt help than put in a stock jet or 1 size up id say

[Cujo909]

Bparker525, I went from a 138 main to a 150 main with the same results. I have this feeling it's got something to do with a header leak, causing it to suck raw air maybe? Or electrical? This really bothers me because with all The Hondas I have owned and do things to I have never had this problem with backfire or idol. The carbs were spot on from factory and when I did a mod I followed the pipe makers jetting with zero issues. I owned like 8 different Hondas, 4 350x's. I fear I have bought satans trike lol.

[6speedthumper]

An exhaust leak can cause jetting issues like you wouldn't believe. I have a customer's 200m in the shop now with the same problem as yours, and it runs like pure crap. I just need to get a muffler for it. Only other way to check for other leaks is to hold several rags over the tail pipe, and force the leak to appear. But, if the system is rusted, you can cause another leak. I'd get that fixed before I go any further. I'd also install a new plug, stick with NGK, best made (not looking for a fight about it).

[Cujo909]

Lol not looking for a fight... Ok I will resume there and see. Thanks a lot for the input.

[CodyRosa]

Where is the exhaust leak? My wheeler has a leak where the header meets the muffler. It kind of clogs itself up with carbon right away though but still it never popped for me from that. Does it idle find when its hot? Not warm I mean hot, like if you ride the thing hard for an hour hot. If it doesn't idle your head gasket is more than likely out. You said it idles high? Do you have any air leaks in front of the carb at the intake boot? I know when mine popped and whatnot it was to lean. I run mine dark brown so its just a tad rich. I don't know much about this situation but I figure those are some problems that should get fixed.

[Jason125m]

While it is running spray carb cleaner all around the intake boots and carb, if any change in idle you have an air leak, which is what I think is happening.