Almost there

[spayne83]

The wiring is 90% finished (just need to finish the seat and mount the lights) and the carbs have been gone through repeatedly, but I am still getting backfiring at anything over 1/2 throttle.

The carbs are set to stock specs (137.5/42.5 Genuine Mikuni) with the exception of plastic floats set to 25.7mm. I wasn't able to sync the carbs because it will not idle at 1100 but when it was close each carb was within 1-2 in Hg of each other at ~1000 before it died.

I did the coil repower (http://www.wgcarbs.com//index.php?op...w&id=Itemid=89) and removed the pod filters and installed a 78 mech advance because mine was sticking and I replaced the vacuum advance since mine was bad. I also spliced in new coil pickup wires and set the gap per the manual. I went for a ride and the problem of backfiring was significantly better, but I can still get it to backfire on command by twisting the throttle and the acceleration is sluggish/non-existant. It will rev all the way to 8000 under 1/2 throttle.

Today I switched out the plugs for some fresh side gapped plugs and all the old plugs except #2 were black which jives with the backfiring. So I went for another ride and the backfiring was almost gone there was just a flat spot and some slight popping at WOT. There is still poor acceleration at all throttle openings but it will rev freely in neutral and return to idle.

With that said I have a few questions:

Since it revs freely in neutral and only backfires at over 1/2 throttle should I lean out the needle jet one slot?

There is disagreement over what height to set 79 carbs with plastic floats, but based on the plugs I don't think that I should use the 23mm specified by the floats. Will float height lean out all throttle positions?

It will idle just fine at 1200-1300, but trying to adjust it lower than that is very problematic. I used my timing light set to 2 cyl mode to check the rpm. The bike was warm but it would die down to 800-900 rpm and then bounce back to 1200. Is it absolutely necessary to have the bike at 1100 rpm to sync the carbs? Can I time the bike without it being able to idle below 1200?

I am so close that I can smell it, and it was great fun riding today even though I was scared of backfiring and it was really only a tuning run. I just want to have the bike finished up so I can start to enjoy it.

[spayne83]

I just went for a ride and it is definitely just the midrange that is the issue. I could roll on the throttle and it would pop until about 6k and then clean up and pull to redline. So to me that sounds like a timing issue because it is around 5.5k that the bike reaches max advance.

The other issue is the high idle. I just tried lowering it and it would stumble a bit around 1500 and any lower it would backfire. Here is a vid:



So how do I time the bike if I cannot get the idle down to 1100? It is only backfiring out the right pipe, so that is 2 or 3 and there is white smoke that follows. I'm not sure if it is related to the midrange problem, but it is definitely an issue.

Other than that it rides ok. Off idle is fine and cruising is ok.

[motoman]

The wiring is 90% finished (just need to finish the seat and mount the lights) and the carbs have been gone through repeatedly, but I am still getting backfiring at anything over 1/2 throttle.

The carbs are set to stock specs (137.5/42.5 Genuine Mikuni) with the exception of plastic floats set to 25.7mm. I wasn't able to sync the carbs because it will not idle at 1100 but when it was close each carb was within 1-2 in Hg of each other at ~1000 before it died.

I did the coil repower (http://www.wgcarbs.com//index.php?op...w&id=Itemid=89) and removed the pod filters and installed a 78 mech advance because mine was sticking and I replaced the vacuum advance since mine was bad. I also spliced in new coil pickup wires and set the gap per the manual. I went for a ride and the problem of backfiring was significantly better, but I can still get it to backfire on command by twisting the throttle and the acceleration is sluggish/non-existant. It will rev all the way to 8000 under 1/2 throttle.

Today I switched out the plugs for some fresh side gapped plugs and all the old plugs except #2 were black which jives with the backfiring. So I went for another ride and the backfiring was almost gone there was just a flat spot and some slight popping at WOT. There is still poor acceleration at all throttle openings but it will rev freely in neutral and return to idle.

With that said I have a few questions:

Since it revs freely in neutral and only backfires at over 1/2 throttle should I lean out the needle jet one slot?

There is disagreement over what height to set 79 carbs with plastic floats, but based on the plugs I don't think that I should use the 23mm specified by the floats. Will float height lean out all throttle positions?

It will idle just fine at 1200-1300, but trying to adjust it lower than that is very problematic. I used my timing light set to 2 cyl mode to check the rpm. The bike was warm but it would die down to 800-900 rpm and then bounce back to 1200. Is it absolutely necessary to have the bike at 1100 rpm to sync the carbs? Can I time the bike without it being able to idle below 1200?

I am so close that I can smell it, and it was great fun riding today even though I was scared of backfiring and it was really only a tuning run. I just want to have the bike finished up so I can start to enjoy it.

Irregardless of dissagreement, 23mm for the plastic floats no matter if early or later carbs. Actually if you can get carbs close so idle is LOW as possible(800-900) for carb sync, then after done and ridden some, set idle to nornal 1100rpm. Modifying and 'side gapping' plugs is a mod to eliminate. Have all things close to stock as possible for a baseline tuning process BEFORE any mods are done. Out of sync and too low of float levels ARE causing your running issues at this point, period. ALL eight floats HAVE to be set IDENTICAL setting level.Close is NOT good enough. Eliminate the mods, anal with float settings, sync, reset idle mixtures, re-sync and if all was done CORRECT, you'll be golden.

[spayne83]

Just reset the floats to 23mm (extremely anal about it) and took it for a ride. Same issue, but it would not stumble through the rough midrange. I had to slowly roll on to full throttle around 5-6000 and then it would pull up to 8000. Tomorrow I will change the spark plugs for stock plugs gapped to .030 in and try it again. I am just wanting to strictly make only one change at a time, so that I can pinpoint what the issue was. Then I will sync and time the bike (if I can get it to idle around 1000).

[motoman]

Just reset the floats to 23mm (extremely anal about it) and took it for a ride. Same issue, but it would not stumble through the rough midrange. I had to slowly roll on to full throttle around 5-6000 and then it would pull up to 8000. Tomorrow I will change the spark plugs for stock plugs gapped to .030 in and try it again. I am just wanting to strictly make only one change at a time, so that I can pinpoint what the issue was. Then I will sync and time the bike (if I can get it to idle around 1000).

Initially, three changes got you to the point you were......lesson learned. Checking the timing when one doesn't know whether it had previously been messed with is a good thing(set at what the manual states). While cover is off, next check would be to make sure vacuum advance assembly is 'floppy' loose(this may attribute to having to apply gradual throttle/load). If all is good there, then proceed to carb idle mixtures, then sync.

[Gallaecus]

hook the timing light on the no 1 wire and point it at the timing plate.
the timing is probably good, cuz these bikes generally dont require you to set the timing. take your valve cover off and see if the timing marks line up on the cam gear. per manual. check your valve clearances. check compression.

its probably your carbs anyway.....

[oldnortonrider]

Spayne; here's something you might try: TURN the pilot mixture screws out 4 full turns; on all four carburetors; now sync 'em; I'll guarantee your high idle problem will go away; probably even before you sync it. AND you'll be able to get it to behave and run at whatever low idle rpm you might want to leave it at. IF THIS WORKS; it's cuz yer 30+ yo butterfly seals are allowing to leak a small enough air into the throat of the carb, that it's way lean, and making it much more temperamental at the low rpm. What I'm suggesting is fast, easy, and simple; if it doesn't work, you can change the pilot mixture screws back where you had 'em.

[TopCatGr58]

Hey there Spayne,

Motoman/Brant has given you some good advice. Some things that you stated along with your signature and bike mods caught my eye.

Okay, stock 79 carbs with stock jetting...however you're running indy pods and aftermarket 4-2 pipes...with unknown baffles or not?? This setup is asking for much more main jetting if also not 1 size up pilot jetting. Like Oldnorton said, you can probably turn your pilot screws out several turns to get close to the fuel it will need in the pilot circuit.

Your signature says Pod filter MOD with Emgo pods? Yet, in the video I can see the pods mounted directly to the carb inlets...no mounting mod there, so are you saying that because it has the Emgo pods that it is the Pod mod, vs. the OEM airbox?? Those filters have a prominent mounting lip and can obstruct the airflow at the inlet bell....folks have experienced excessively rich conditions because of them, and that's why we have suggested/recommended the Velocity Stack type mounting mod for the pod filters, both to ensure that the inlet bell ports are not blocked, and to help straighten out the airflow from the filter to the carb...which has also been reported to increase low end response.

SO....yes, get the floats right, but I think you'll be needing a few sizes up on the mains....most folks with similar intake/exhaust mods have used the 145's or at least 142.5 for the main jet size, and up to 45 for the pilot jet.

Good luck, keep at it!

T.C.

[motoman]

Good observation T.C.! Makes for several changes made, and as T.C. stated, those style pods are #1 suspect that definitely need corrected before diagnosing farther.

[spayne83]

Hey there Spayne,

Motoman/Brant has given you some good advice. Some things that you stated along with your signature and bike mods caught my eye.

Okay, stock 79 carbs with stock jetting...however you're running indy pods and aftermarket 4-2 pipes...with unknown baffles or not?? This setup is asking for much more main jetting if also not 1 size up pilot jetting. Like Oldnorton said, you can probably turn your pilot screws out several turns to get close to the fuel it will need in the pilot circuit.

Your signature says Pod filter MOD with Emgo pods? Yet, in the video I can see the pods mounted directly to the carb inlets...no mounting mod there, so are you saying that because it has the Emgo pods that it is the Pod mod, vs. the OEM airbox?? Those filters have a prominent mounting lip and can obstruct the airflow at the inlet bell....folks have experienced excessively rich conditions because of them, and that's why we have suggested/recommended the Velocity Stack type mounting mod for the pod filters, both to ensure that the inlet bell ports are not blocked, and to help straighten out the airflow from the filter to the carb...which has also been reported to increase low end response.

SO....yes, get the floats right, but I think you'll be needing a few sizes up on the mains....most folks with similar intake/exhaust mods have used the 145's or at least 142.5 for the main jet size, and up to 45 for the pilot jet.

Good luck, keep at it!

T.C.

I originally had 145/45 jetting, but I wanted to get it all back to stock and then move on. This whole process feels like chasing my tail a bit.

The timing is definitely off because I was trying to time it previously with the wrong TCI. What do you mean the vacuum advance is floppy and loose? The mech advance is loose enough to move with my fingers and it snaps back to the starting position immediately when pressure is released. The vacuum pod was just replaced and it does function properly reaching max advance around 7 in Hg.

It's hard to see from the video, but here is a before picture with the pods mounted right to the carbs:



In the video around 14 seconds you can see the chopped stock velocity stacks crammed into the pod filters to avoid the nasty lip they come with. Trust me they are there.

I'll go ahead and try what you guys suggest and report back. Thanks for the help.

[spayne83]

I tried turning out the screws to 4 turns out and still no dice. Here is a video:



I was wondering if anyone can tell me what the little pops are that I hear? It is constant at idle even when idling at 2500.

I also encountered a new problem







There is a thick layer of oil in the exhaust. I forget what viscosity oil I put in last time (may have been 10w-30) but I was wondering if it is just thinning out enough to slip past the seals. That would explain the backfire from only the right side as the left side is dry.

Still not able to do the timing because of the idle issue. Should I bump up the jetting to 145 and 45? Pulling in 3rd gear the bike will not go past 6500 rpm. It just doesn't seem to have any power left, so I am thinking that I need to go back to the 145/45.

[jetmechmarty]

I have an XS650 that pops on the right side. That's the side that has a hole in the muffler. Have you checked thoroughly for leaks? (vacuum and exhaust)

I wouldn't be running 10W30 in that thing.

[spayne83]

I haven't checked for exhaust leaks, but I did spray previously with carb cleaner and found no leaks.

I verified that there is oil on the #4 spark plug and maybe a hint on #3. Could the 10w30 cause that? Never had a problem before about a week ago, but it might have gotten really hot riding around town.

[Gallaecus]

your valve clearance must be correct before you can accurately tune the carbs.

you should be able to set the timing regardless.

you might want to check compression cuz oil out the exhaust is a sign of worn rings or leaky valves.

[spayne83]

All the valves are within specs.

I will do a compression test tomorrow, but I did one when I first got the bike and one cylinder was down, but it has never leaked before.

I'm going to finish changing the oil and then see if that fixes things.