Carb problems...

[Prairie Dog]

Sled was running pretty decent except for a bit of top end bog. I changed out the jets from 162.5 to 165 and reinstalled the carbs.

The engine sputters at partially open throttle just when it gets under load. It will rev, but doesn't pull worth a darn. Then it backfires and runs miserably at half throttle to get back to the shop.

It seems to me that the slides aren't opening properly. I took the carbs back off suspecting a vacuum leak. I rechecked the mains, blew everything out and put the carbs back on, being careful to seat them in the rubbers properly.

I tried different needle settings, springs from one end to the other. Not much difference. It idles fine and throttle blips in the shop just fine. It's only under load that it starts to sputter.

This sled ran almost perfect until I took the carbs off the first time. I must have done something unintentional. I did not blow out the pilot jets when I had the carbs off. I also don't know if the TPS will cause this syptom. I might have unintentionally readjusted it?

The only other thing I can think of is that I used Lubriplate white grease to lube the o-rings on the main jets. It may have gobbed off and floated into the smaller jets and may be plugging one or more.

Any help is appreciated. Otherwise off to the shop tomorrow.

 

[grader]

check to make sure the float bowls are tight when finished working on carbs. remove and clean pilot jets. burn paper off a twist tie and pass it through them and look through when done. use small tube on carb cleaner can and blow out all circuts. if you removed carb tops make sure the rubber diaphrams are not pinched.

 

[Prairie Dog]

You know, I've done everything but that more than once. Needle heights, springs, tps, tors, mains. I'm kicking myself because I had the carbs off earlier today thinking main jet plugged and didn't check the small ones.



If anything, I'm getting good at it. Whatever happened happened the first time I changed the mains and hasn't gotten any better since. It almost has to be dirty pilot jets because I've done everything else, multiple time.

Thanks

 

[Blue shadow]

Make sure your plug caps are seated down all the way.They do come up at times.

 

[Prairie Dog]

Make sure your plug caps are seated down all the way.They do come up at times.

Thanks, did that. I had put in a set of the cr10ek's and took them out right away when this started. No difference. I'm manning my business probably for the rest of the day and won't get to clean those little jets til later or tomorrow.

I'll let youse know.

 

[kenlacy]

Did you sync the carbs?

 

[Prairie Dog]

Did you sync the carbs?

We did that the other day. I'm not sure if it needs done every time. Frankly this symptom is like half the engine cutting out when you throttle it.

 

[grader]

something else to check is the airbox. spray inside flanges and outside of carbs with wd40 before installing. check the clamps on each flange to make sure they havent moved out of place. also check the 2 vent lines are not pinched.

 

[black john]

carbs

ckeck the slides and make sure that one is not broken. the pilot vanish over very fast let them sit over nite in clr then clean them out as the varnish is hard to see and just when you think there clean anther pcs of varnish shows up. mine came this way from yamaha

 

[Prairie Dog]

I feel stupid....

I put the 162.5 jets back in and raised the needles to 4 and holy cow, I've got a smokin sled on my hands. Top end bog is gone.

I never thought 1 jet size would make an otherwise good running engine run that bad. Sorry to trouble you guys and thanks for the info.

End of post.

 

[Trxster]

You didn't accidentally replace the wrong jets did you???? 1 Jet size would not make a significant difference but when I first threw my jets in I replace the starter jets and it ran sooooo lean with the ECP I had to hold the choke full open to run at mid throttle.

T

 

[Prairie Dog]

No, apparently, it threw the carbs out enough to make bad symtoms. Live and learn.

 

[SUPERTUNER]

I feel stupid....

I put the 162.5 jets back in and raised the needles to 4 and holy cow, I've got a smokin sled on my hands. Top end bog is gone.

I never thought 1 jet size would make an otherwise good running engine run that bad. Sorry to trouble you guys and thanks for the info.

End of post.

1 jet size on the main jet did not cure your problems. I would say the needle being richened helped more than the main jet. You had the same problem with the 162.5 main jets in. Gld you got it running good though.