Not running on all four!! HELP!

99YAMAHAVMAX · Jul 14, 2023

Semi239 said:
Well I have a great update!

I retested the compression at WOT and scored wonderfully. 170psi+ on all cylinders. I am glad to have that ruled out.

I pulled the rear valve cover and found all valves in spec except for a single intake valve on cly3(1 thou tight). I also found an odd discoloration on the cams on cyl1. Has anyone seen this before? Mabe lacking oil? it's not on the other cams over cly3. see pics

Being that we got good compression I didn't do the leakdown test. I turned my attention back to the carbs. With the airbox off you can feel the strong vacuum on cyl2. But all the others have a very poor draw. Also, none of the needle slides are pulsing until I get the throttle close to wide open. While messing around with it by capping off the carb with my hand and taking it away I was able to get cyl 4 to draw well and saw a spark in rpms getting a bunch of fuel. But without my fiddling with it, the draw dwindled back down to nothing. It seems like there is so little air being moved thru the carbs that cyl3 isn't even getting enough fuel to fire and cyl1+4 are getting just enough to stay alive but are very very rich.

While I was there I shot brake clean at all of the boots and boost manifolds and found no cracks that drew in air enough to spike rpms. I will pull all of them and inspect them when I take the carbs off again.

What should I be looking for in these carbs? Obviously large debris blocking passages, but are there any problematic points in these carbs that should have special attention? I have had these carbs off 3 times(twice by me and once by a shop) and haven't found any glaring issues.

What do yall think?

37.5 pilot jet inside the jetblocks under the rubber stopper causes the most problems as it has the smallest passage---under the gasket the passages through the carb bodies need clearing also. Float settings are very important also.

Semi239 · Jul 14, 2023

Bill Seward said:
Actually it was a huge leak, the right 2 carbs popped off the boots

Wow! yea that will do it. I'm fairly certain they are seated fully, put all my weight on them, and felt them pop in. And since I couldn't find where it was drawing in air at the boots, makes me think they are seated

99YAMAHAVMAX said:
under the gasket the passages through the carb bodies

I shot carb cleaner thru all of those passages when I tore it down last time but I will double check there isn't anything new in there.

Semi239 · Jul 29, 2023

Well boys i figured it out.

Pulled the carb again and found the issue. multiple clogged passages. The main offender was the air passages but I found others clogged. see attached,
I got an ultrasonic cleaner and they are sparkly clean now! Also replaced all soft parts with a K+L kit.
Got a DigiSync and got it purrring like a kitten! That first ride back was euphoric!!

On top of the above I got my seat from Sean Morley put on and corrected a coolant leak under the radiator.

Thank you all for the help! its always the carbs

99YAMAHAVMAX · Jul 30, 2023

Semi239 said:
Well boys i figured it out.

Pulled the carb again and found the issue. multiple clogged passages. The main offender was the air passages but I found others clogged. see attached,
I got an ultrasonic cleaner and they are sparkly clean now! Also replaced all soft parts with a K+L kit.
Got a DigiSync and got it purrring like a kitten! That first ride back was euphoric!!

On top of the above I got my seat from Sean Morley put on and corrected a coolant leak under the radiator.

Thank you all for the help! its always the carbs

Usually the culprit-also that #1 carb with the three nozzles you hold 2 of them closed and shoot air through the float needle holder.

dannymax · Jul 31, 2023

Semi239 said:
Well boys i figured it out.

Pulled the carb again and found the issue. multiple clogged passages. The main offender was the air passages but I found others clogged. see attached,
I got an ultrasonic cleaner and they are sparkly clean now! Also replaced all soft parts with a K+L kit.
Got a DigiSync and got it purrring like a kitten! That first ride back was euphoric!!

On top of the above I got my seat from Sean Morley put on and corrected a coolant leak under the radiator.

Thank you all for the help! its always the carbs

Good deal. By the way, you may want to hang onto those 'cracked' oem coils. The cracks you are looking at are only in the thin outer rubber wrap...the coil itself is underneath and well sealed in epoxy. Trim the ends of the plug wire to shiny copper, disassemble, clean and di-grease all contact points in the plug caps, ohm the resistors and put them away in case a cop fails.