rebuilt 28's. poppin thru pod filters! why?

old_skool_77 wrote:

took this bike to have carbs rebuilt and tuned properly at a bike shop. should I take it back???

Any decent tune-up would include assuring valve clearances being to specs.

Before deciding about taking it back, would personally measure the valve clearances. Being too tight would indicate having received less than a proper tune-up. And raise concerns about the shop's competence and integrity if for example you supposedly received more that new plugs and a dose of SeaFoam plus some carb pilot screw fiddling.

Pinging NOT under load -- okay, but would remove and examine plugs anyway to get an idea of what's happening inside the combustion chambers.

Good Luck!

The pinging he is describing is under load:

only when i lean foward to hold on and hit the gas is when i hear it

Along with popping during cruise conditions.

I would check the timing, it sounds like it could be too far advanced. Also, the pilot jet of 117 doesn't sound anywhere near right. Should be 15, 17.5, 20, Etc. Even if they left of the decimal, which happens, there should be no 11.7 pilot jet for VM's.

My second guess would be that it is too lean, either due to a vacuum leak or jetting.

Finally valve clearances.

Bottom Line: If you paid a shop to tune it, then it should run right when you get it back. It does not.

I would take it back, or get my money back.

With the air popping back out of the carbs, I am thinking that it is a air leak.

I had an air leak on my bike and that was the symptom, every 15 sec it would spit out of the carbs... it kind of made a "ppffffffhhhh" sound..... 15 sec and then "ppfffffhhhh" . My bike would also only run with the choke up.

After I solved the problem the popping stopped and the bike runs perfectly.

I checked the timing and it was at its proper setting. as far as the pilots, my mistake but they are 17.5. I was told by the shop that worked my bike, that want me to bring it back and they adjust the slide needles down to the fourth notch to richen up the mix. does this seem right? The fuel mix screws are set to 1 1/4 turns out. If I turn these in 1/4 to 1/2 turns in should this compensate for the mix compared to the adjustments of the needles? As far as vacumm leaks are concerned. Everthing as far as gaskets and and o rings and hoses and such has been replaced with new stuff.

old_skool_77 wrote:

I checked the timing and it was at its proper setting. as far as the pilots, my mistake but they are 17.5. I was told by the shop that worked my bike, that want me to bring it back and they adjust the slide needles down to the fourth notch to richen up the mix. does this seem right? The fuel mix screws are set to 1 1/4 turns out. If I turn these in 1/4 to 1/2 turns in should this compensate for the mix compared to the adjustments of the needles? As far as vacumm leaks are concerned. Everthing as far as gaskets and and o rings and hoses and such has been replaced with new stuff.

if it were me id go with #20 pilots and 4th clip the needles.....if they are willing to take it back in and fix it, do it....service like that is getting rarer these days.....1 1/4 turns is right and messing with that will do a little, but its not gonna replicate 4th clipping the needle.....i m sure others will chime in...

Me too. My plan was originaly was to go with 20 pilots and 130 or 132 mains, but the shop guy said the stockers would be fine so I let him run the show. Think that I will move the slide down with the 20's and the 132 main or just the pilots and the needles knocked down?

old_skool_77 wrote:

Me too. My plan was originaly was to go with 20 pilots and 130 or 132 mains, but the shop guy said the stockers would be fine so I let him run the show. Think that I will move the slide down with the 20's and the 132 main or just the pilots and the needles knocked down?

132 main sounds awfull big to me....what are specs and what kind of pipe/baffle? and 4th clipping will raise the needle allowing more fuel in....

Your Bike is fine !! K.I.S.S
4th clip should be the fix For the popping.
Your just running a little lean on decel.
This is very common.
The Fuel mix screws are for a different circut, you should leave those alone.

What Tackrav said:
"Bottom Line: If you paid a shop to tune it, then it should run right when you get it back. IF It does not. I would take it back, or get my money back. "

I can reproduce the EXACT same on my Keihin CR's....

Just recently had to go through emissions... To pass, I had leaned the slow jet screws (Pilots) way out which causes popping out the carbs. So turned them back in just a tad (RICHER) thus end of popping and got through emissions.

Since you just had these carbs worked on, possibly wrong size pilot jets if popping at idle as well or they aren't calibrated correctly.

If popping at 1/4 to 3/4 throttle then needle jet clip position, running too lean. Or wrong needle jet itself.

What do the plug insulators look like?
Black, brown/tan or white....

Did you have this problem pre-carb work?
If no then most probably not your valves or timing.

There's also that I may have missed something that was already mentioned so I'll shut up now.... lol!

OMR

Not sure what your compression is or other factors to the valves, coils etc., but on my stock '79 MkII engine running a cheap-azz MAC that's opened very slightly, and pods, my pumper 28's have 17.5' and 120's I think. The mains might be 117's, I'd have to dig around to see what exactly I landed upon for the correct setup. Anything larger than 120 on a stock MkII unless the pipe is just about full open is too much. I'm set on the 3rd clip too if I remember correctly. You have to match the roll off of the pilot to the needle to the mains, no big steps. Also remember that lean is mean but don't hole a piston, check those plugs for color.

Do you ride with your legs hugging the tank or out some? If you ride with them out some, the outside two carbs will bog/lean and pop if you twist it up. Get used to riding with your knees on the tank sides and you won't feel that power drop and pop/surge. Some guys fab little shields for the outside pods to help cut the blast from your legs acting like scoops.

If you're still having fits trying to set it let me know and I'll dig through my notes or through my leftover jets to try and determine where I ended up, it's easy to lose track of what you did a year ago after trying several different setups to dial it in right.

117 mains and 17.5 pilots should be more than enuf for a stock motor.add to that raising the needles to 4th notch it should be good to go.I ordered the same jet sizes from Redline and they told me all i really needed was to raise the needles and leave the 115s and 15s alone.now i have the 117.5 &17.5 combination with needles in 4th notch and have no problems.(stock 79 LTD 1000 with 28 pumper carbs pods and Kerker with modified(just the end cap) baffle.

All of this information is really helpful and I appreciate all the input. My motor is 1015 cc with and have open pod filters with a sidewinder that is not baffeld. 28 mikuni's with 17.5 pilots and 127.5 mains. Poppin from carbs is happening when i'm at cruising speed in any gear. I put the baffle back in the pipe to see if any changes, but no changes except the rediculously quiet and I hate it. I want to run without it but maybe cut it up and drill some speedholes in it to make it sound the way i want it to.. Anyways, the baffle didnt make any changes to the performance of the motor. A buddy of my fired is kz 1000 up today after we put an open header on it. thing is, the pipe was cut off about where the ignition cover is. The bike sound mean as heck and no poppin or anything. sounded perfect. He has 132.5 mains and 20 pilots with velocity stacks. maybe this is my tweak with the jets to cure my problem? Oh, by the way, my plugs were blck(carbon buildup i'm thinkin).