Will rusted out exhaust cross tube/joint cause backfire & stall?

[JayR]

I've been breaking in my rebuilt motor and the bike has been running beautifully (amazing!) for about 100 miles.

When I put the motor back together I used the original exhaust, which is in poor condition; a Knickle sized hole in the left bottom rear muffler past the cross tube, and the cross tube joint is totally rusted away.

So I patched up the cross tube joint with some hack job crap just to get the bike on the road. It seemed to do the job because as I said the bike was running great - with a bit of a snarl to it due to the shitty condition of the exhaust.

Well I've been babying th throttle ( break in) but today I twisted it all the way open for the first time (nice!) BUT...at th next stop sign the bike stalled out and wouldn't hold idle at stops anymore. AND is backfiring now moderately.

I immediately suspected that the cross tube joint patch blew, and somehow the change in back pressure is causing my new problems. When I put my hand down there now it feels like a 3rd exhaust pipe exit

Before I search eBay for a good condition used exhaust, do you think my diagnosis is accurate - or is something else in play like carbs or something?

 

[weekendrider]

For the cross over I've have used freeze plugs(welded in) to plug the hole. You loose the cross over pipe but I didn't notice any effect on performance.

The hole in the muffler is a different matter to me. If the resistance(back pressure) isn't close to the same will it mess with the vacuum syncing of the carbs?

 

[TwoManyXS1Bs]

I'm thinking the WOT vibrations dislodged some crud that worked its way into the carbs...

 

[JayR]

For the cross over I've have used freeze plugs(welded in) to plug the hole. You loose the cross over pipe but I didn't notice any effect on performance.

The hole in the muffler is a different matter to me. If the resistance(back pressure) isn't close to the same will it mess with the vacuum syncing of the carbs?

Hey WER, did you go with the 1 1/8 freeze plugs and go cup in? I think I will cap the cross pipe first like you did to see if that helps.

I'm wondering too about the carbs. At WOT I think the slides were opened for the first time, or at least for the first time for duration. Weird thing is that about 15 minutes after the problem started, and continued, the stalling at idle stopped. So maybe the vaccumm equalized after getting on it. But I really don't know what I'm talking about at This point

 

[JayR]

I'm thinking the WOT vibrations dislodged some crud that worked its way into the carbs...

Hi TwoMany - Thanks for the advice. Yeah, now I'm wondering if it has to do with the slides being wide open for a good haul for the first time.

Could be that some crud shook loose too. But I derustified the tank three different ways (sheet rock screws/rinse, electrolysis for 24 hours/ rinse, filled tank with rust remover for a couple days, then rinsed with isopropyl alcohol. And sprayed with wd 40! And new petcock and inline gas filter.

Shoot, if something shook loose I give up but anything is possible.

I'll do the freeze plugs first I suppose to see if a sudden decrease in resistance is the culprit, or if further carb investigation is needed.

Cheers gents and thank you.

 

[TwoManyXS1Bs]

I suppose you could drain your bowls into a clear container and look for specks.

Then, there's ignition. Check the plugs...

 

[weekendrider]

I don't remember the size but it worked just like your picture. Just enough interference fit to hold it while I welded it in.

 

[gggGary]

yup drain bowls, seat and reset pilot screws. Even better pull them and spray carb cleaner reassemble, Next on the list is pilot jet cleaning, that pilot jet hole is TINY! By the way these are a do first, when a bike starts acting up out of the blue.