hesitation and backfiring

[randu]

still trying to get my '98 running right. someone abused it but id like to get a few years out of it. thought i had a carb problem so i rebuilt it, cleaned tank and sealed it, changed fuel filter...got it back together, and have exact same hesitation in every gear and backfiring as before i started. is this an air leak? a compression problem, more carb adjustment...im a noob bike mechanic trying to not spend any more than i have to. (already put more into it than i could ever get out) -what would you check next? thank you!

 

[Fire-medic]

I suspect you may have good results from using starting fluid, and spraying it around the rubber donuts above & below the carburetors (above, to the airbox; below, to the VBoost manifold). Also spray around the connection between the VBoost manifold and the cyl heads. An air leak will pick-up the rpm's when you spray that area, and the lean condition caused by an air leak, temporarily increases rpm's as the starting fluid is sucked-through. The starting fluid is sometimes replaced by LP gas. I suggest you be very-careful if you use LP gas, and don't do it inside. I don't use it, myself.

A compression check is easy to do, and the gauge, hose and fitting for the spark plug hole aren't very expensive.

You have a copy of the service manual saved to your computer?

 

[V-Bruce]

Clean the pilot jet
Change carbs boots
Change spark plugs

 

[randu]

I suspect you may have good results from using starting fluid, and spraying it around the rubber donuts above & below the carburetors (above, to the airbox; below, to the VBoost manifold). Also spray around the connection between the VBoost manifold and the cyl heads. An air leak will pick-up the rpm's when you spray that area, and the lean condition caused by an air leak, temporarily increases rpm's as the starting fluid is sucked-through. The starting fluid is sometimes replaced by LP gas. I suggest you be very-careful if you use LP gas, and don't do it inside. I don't use it, myself.

A compression check is easy to do, and the gauge, hose and fitting for the spark plug hole aren't very expensive.

You have a copy of the service manual saved to your computer?

thank you. ill try that. i have the service manual (i think) but seems hard to navigate on laptop. because of that i bought clymer manual. havent dug into it, just got it. replaced doughnuts when i rebuilt carbs..

 

[MaxMidnight]

Before changing anything other than service items make sure the part you are planning to replace is faulty.

If you haven't done a full service then I would do so and never assume it has been done. Can we assume the carbs are balanced?
Have a good look at the HT leads and caps to ensure they are clean and not arcing - easily done at night but NOT in a closed area!
Mr Medic has suggested how you can check the inlet side. If it is the exhaust then I would expect to see evidence of a leak around the various joints.

If you are still left with the problem then check that the carb slides move together as you open the throttle and as a longer shot that you have the correct jets.
An even longer shot is to check the advance unit is functioning correctly.

 

[randu]

thank you! ill try to figure out how to test all that. by HT leads do you mean plugs & caps? it has a steady popping backfire from right exhaust only. does that indicate an air leak? thanks again so much to all

 

[Fire-medic]

Yes. Plugs/caps.

You are correct, the 'popping backfire' you describe is usually a sign of a lean condition. That is often an air leak.

 

[randu]

so after all ive done, rebuilt and checked... i really think that the problem lies in a gap between the engine exhaust outlet and the head/flange of exhaust pipe. it backfires from front of bike as well as one side of tail pipe. trying to get it off and the stud seems bent/crooked, causing a small theoretical open space between exhaust header and engine... can i assume that its a double threaded bolt that can be backed out and replaced? are there compression gaskets out there that can compensate for any gap? as always, thanks in advance for your expert contributions..

 

[cyclejunkie]

Sounds like vacuum leak. Carb manifold boots are probably dried out/ dry rotted.

 

[randu]

just swapped those out...a gap between engine and exhaust head would cause similar right? i can hear it popping in that general area as well...thank you

 

[Fire-medic]

#1 question: its a double threaded bolt that can be backed out and replaced?

#2 question: are there compression gaskets out there that can compensate for any gap?

1] yes, see parts # 6 & 12 1st pic
2] yes see part # 26 2nd pic

 

[randu]

thank you so much. is this "partzilla" website?

 

[Fire-medic]

No Ron Ayres Yamaha in No. Carolina. Been ordering from them for many years. Sean Morley carries a lot of OEM Yamaha VMax parts, and CaptainKyle along with Sean both are always parting-out bikes. Check the classifieds as many members also post up their excess parts, also.

https://www.ronayers.com/oemparts/l/yam/50045c0bf8700209bc7942e9/2007-v-max-vmx12w1-parts

 

[MaxMidnight]

If you do replace the stud use permanent threadlock on the cylinder head side. It will lessen the likelihood of it coming out with the nut should the exhaust need to be removed at some time in the future.

 

[randu]

will do. thanks!