what causes sneezing, low rpm misfiring, and won't idle?

[pcrussell50]

this is on one of my v4 crossflows with an ordinary choke, not that newer quick start enrichment solenoid. it runs GREAT, at higher rpm if i can get it there without dying, but i can barely keep it running at 1500rpm--where it has an irregular miss, and occasional sneezing. i rebuilt the carbs, including changing the core plugs fairly recently. i did a compression test this afternoon and got:

128-134
125-128

as viewed from behind.

i have not done a leak down test.

i'm seeking some guidance as to where to start my troubleshooting. i "feel" like it's a fuel problem, or an air leak or broken reed. i don't "feel" like it's electrical--but feelings aren't worth squat in a deterministic mechanical system.

i'm tempted to tear into the carbs again just to make sure--unless someone here advises me otherwise.

-peter

[EMDSAPMGR]

Very nice Stream! Usually a crossflow occasional miss at idle is termed a lean sneeze. This is a carb/fuel issue. A good internal cleaning, esp. of the idle passages in the carb body will take care of it. You’ve indicated that’s been done. If the carbs are known to be spotless internally,you may need to look at the idle jets in the carb. Engine modifications, (such as adding composite reeds, or carb swaps, etc.) change the airflow through the carb and can change the air fuel mix. You can correct that by changing jets to flow slightly more fuel through the idle circuits. <o></o

[99fxst99]

One more thing to check is to make sure the carb butterflies are both closed at idle. If one is standing open it tries to run on that one, dragging the other carb/two cylinders with it. This is more so on V6 crossflows, but applies to V4s as well. Loosen the linkage between the carbs and see if one carb snaps shut.

[Riverman]

Another member recently had the same problem with his V4 and the problem turned out to be loose (worn) throttle shafts.

[racer]

It may be leaking at one of the core plugs you replaced, try some gasola around them or even finger nail polish. Throttle shafts are a problem on the older engines.

[pcrussell50]

It may be leaking at one of the core plugs you replaced, try some gasola around them or even finger nail polish. Throttle shafts are a problem on the older engines.

on edit: i think i've found what you are talking about. it's this stuff here, right? stuff is hard to find in small amounts and hideously expensive because it only seems to be available through volume distributors.

al,

do you really mean gasola, or is it gasoila? i've never heard of this stuff. can you (or anyone) give me a link or something specific. i _did_ scratch/gouge one of my core plug bores removing an old one, so I'm suddenly VERY interested in this product. Where can I get it? NAPA?

i've been looking at gasoila's web site and they make a huge variety of stuff, so it's hard to guess which one you are speaking of. that said, one of the things they offer is a red, hard setting, varnish-style sealer.


as for too much play in the throttle shafts, how is that tested for? if they "feel" right is is safe to assume they are ok? or if they "feel" loose then they are not ok?

-peter

[racer]

What you pointed out is correct I forgot the i. It is available from brp dealers. If they feel loose they are and need to be repaired, if minor you can richen the idle circuit.

[pcrussell50]

thanks for confirming. is the throttle shaft repair for pro's only, with specialized equipment?

-peter

[rev.ronnie]

Sounds symptomatic of a reed problem..

[mn808gade]

bleed hoses,intake gaskets, reeds. clean motor-run @ night w/bright light,look for sneezes.

[spongy62]

Check the Reeds

[perfmarine1]

Could be the e-10 fuel has leaned out the idle,make sure the idle jets are clean,and or increase to larger size idle jets.

[930turbo]

Take the return springs loose then check for wear. Once I did that I discovered my throttle shafts were very worn. I installed orings on the port side up against the carb bodies as a temporary fix on two of the four cylinders and the problem was all but resolved confirming this is the issue. I am still trying to source the shaft repair locally for a proper rebush of the bodies.

[Sheermagic12]

Check carb to intake gaskets mine were leaking changed to new ethanol gaskets solved problem.

[pcrussell50]

ooops. forgot to finalize this thread.

took the carbs off and disassembled them and cooked and shook them, (heated ultrasonic cleaner), in kerosene. re-assembled them, this time, following al/racer's advice, and sealed the core plugs with finger nail polish.

in short? she's back running right. woot.

thanks for all the input, guys.

-peter