Bike wont start and coughs when throttle is opened

[Dirtybird]

So i have been working hard on getting my dirtball bike to run lately. (Keep in mind this bike started up fine last fall). I have replaced the stock carbs for the Murrays 4 to 2 mikunis, fixed my starter clutch issue with an r6 clutch, just put in fresh oil and filter, changed the plugs and checked for spark, fully charged the battery and put fresh fuel in the tank. Last fall i tried running the bike on pods and it would start fine, rev fine, but under load it only would rev up to 4k rpms (naturally because of no air box).

Now when i go to start it the bike cranks over fine without the grinding noise of a loose bolt on the starter clutch but she just wont fire (correction: it did actually fire once and the idle went up because i had turned the screws in too far and the chokes were on) backed the idle off a bit and tried again with zero luck. Also as it is cranking if i twiat the throttle at all the left side carb spits a harsh puff at me through the filter. (Literally everytime i twisted it) someone please help me before i break something or just sell the bike out of frustration. :-(

 

[amc49]

Has anybody ever run a compression check on this motor yet? The spitting back is either a valve leaking or the plugs are already fouled and shorting down the sides to not start. It also makes them spit out the intake.

Yank plugs and see if any are wet or black or both.

Unless the carbs came prejetted (and I mean pretty dang close) for the EXACT APPLICATION expect fits like this. Saying so and truly being so are two vastly different things. But then I am prejudiced against that setup, it is wonky and throws away 10 hp. right off the bat. That's enough for me to walk away instantly.

You already see some of it, started with the 4 carbs and look at it now. If you are not a jetting expert you are sunk.

 

[Dirtybird]

Update: So I called SpeedmotoCO. and found that my carbs were on the wrong sides of the engine (the right one needed to be on the left side and the same for the other.) The cough is now gone but I did notice when trying to start the bike the Main wire from the positive on the battery to the Solenoid was sparking badly. found the wire had an exposed section and might be jumping current to the battery box. Gonna replace the wire/solenoid and try again. Thinking i'm creeping up on it though. pretty sure it's not a carb issue and it did fire up before with this configuration.

P.S. with these DOHC CB's is it possible to get the two plugs for the two spark units reversed or are these able to go on either just as long as they are plugged in? These are the only two plugs that I can see potentially being backwards and maybe not firing the coils when they should be.'



And I did replace the plugs as to AMC's comment. they were the NGK iridium plugs that were in it before and seemed pretty fouled. Put brand new NGK plugs in but they are just the base ones (D8EA)

 

[amc49]

The spark units do not care which plug they are plugged into.

If the compression is low enough you will fight plug fouling until you fix the issue. Firing the engine up isn't spit, a dead one will do that.

 

[Dirtybird]

Then tomorrow I shall get a compression tester just to try and rule that out. What psi should the cylinders be at to be good?

 

[amc49]

Book spec is 170 psi. Throttles held wide open and all plugs yanked. Hot battery to spin engine well.

100 is dead. 130 and higher runs better the higher you get. 120 will run but not spectacular.