pilot circuit tuning of my 79GS750 -pods/4into1 V&H

[coltrain]

I'm experiencing some trouble here with my tuning. The basics have been done such as the oring replacement in the carbs, and intake boots, valves adjusted, ign timing etc. The carbs have been synced with a morgan carbtune several times as well.
Using the search feature I found from previous responses to bikes similar to mine that the pilot should be 17.5, the needle clip on the richest setting (the bottom slot on the needle) and I went with a 127.5 mains which all I think are spot on. She pulls HARD at WOT and in the 1/3 + throttle positions. The pilot circuit is where I am having trouble. I even have a colortune, and I can't get it right. It looks good but then I ride and it stumbles at 1/16 - 1/8 throttle. Once I get past that position on the throttle she flies. When I look at it with the Colortune and twist to the 1/8 throttle position I see it get really rich. Set it back to idle and its nice and bunsen blue. Once I just barely get on the throttle it seems to get rich.
I have tried my fuel screws at 1 turn out, and my air screws to the best RPM but I am finding that I am only about a 1 and 1/4 turn out on the air screws. I've tried the fuel pilot screws everywhere. to .75, 1, 1.25, 1.5 turns out. Can't seem to get rid of the slight stumble out of my low speed cruising. I'm VERY close though! Just looking for some help.. suggestions, advice.. someone who has my same setup :-D

Lean out the pilot fuel screws some more? Try another sync? -since I have made adjustments with the air/fuel screws... I didn't mess with the needles since my last sync..

[Mark M]

Lean out the pilot fuel screws some more? Try another sync? -since I have made adjustments with the air/fuel screws... I didn't mess with the needles since my last sync..

I can't help specifically with the VM carbs (I have only worked on CV carbs myself), but your synch will not affect this much at all. I have jetted two bikes without more than a bench synch to start, then a full synch after jetting was done and it was no problem.

You could try the choke test as well, to confirm that you are going rich, but if the Colortune says rich, it probably is. In that case, leaner is the only way to solve it. Hopefully Keith chimes in at this point and sorts it out properly for you.


Mark

[renobruce]

Your pilots should be 15's, not 17.5's. Sounds like you are rich on the pilots.

[coltrain]

Yeah I thought about the pilots being too rich. Most threads I read with pods/4into1 with this 750 is a 17.5 pilot jet with fuel screws set at 1 turn out and the air screws at 1.75, and my bike seems lean with that setup.. if I richen the air screws to just over a turn out she gets better. My plugs have a white tip and but the porcelain white and most of the bottom around there is black.

Have any ballpark jetting for the fuel and air screws with a 15 pilot? Considering my setup and all..

many thanks for the help!

[hampshirehog]

What throttle valve cutaway have you got? The 750s over here had either 2.5 or 1.5 depending on the model.

When you twist the throttle with a colortune it should always momentarily show rich (if the carbs are set up right). What you need to do is hold the throttle steady for a few seconds to let the mixture 'settle down'. If this means the revs running away whip off a plug cap and run it on 3 (or even 2) cylinders to prevent the revs climbing.

[coltrain]

I dont know the valve cutaway size but I would be willing to bet it is the stock size that came on these bikes. Is it stamped on the slide? I can check it out next time I have them carbs off.

I put in the 15 pilot jets today, and I'm now in the process of tweaking. Hard to get it nailed down.. would love to see what someone else is running with my setup.. For a minute there I was tuning forgetting to put the damn vacuum hose back on. Its all there now and air screw likes to be only half a turn out... I reckon take the fuel screws out to about 2.5 and see if it likes that. I've had em out to about 2 turns out now.

[coltrain]

Just an update.. I worked on the bike til I couldn't work no more. I ended up with the fuel screws out at about 2.25 and air screws out 1 turn. No sputter so far but we'll see after a ride, and go through the gears. It started raining so I will have to test ride tomorrow. Still not totally sold it should have the stock 15 pilots yet.

I will update with what I end up with.

[TheCafeKid]

For sure the pilots are too large. My 77 750 project has 17.5s in it now, and starts DEAD COLD on one kick with no choke. A sure sign the pilot circuit is rich. Go back to your 15s, needle clip in the 4 slot down from the top. Airscrews you'll have to tinker with, but as of right now i think you are WAY off base on the fuel screws.

[coltrain]

Josh! Where ya been!

Still haven't gotten your 77 on the road yet? I'd love to know where the fuel screws should be so I can have a good baseline or start. Your suggestions for the needle and mains were money. I tried my bike with the needle clip on the second notch up (4th setting?) and would hardly rev. Its definitely the clip on the bottom or richest slot.

I had almost bought a tank of yours a few months back. Well I finally have a tank all painted.. and getting it on the road. I need to take some photos for you guys.. I will get on that asap.

[TheCafeKid]

Still haven't gotten your 77 on the road yet? I'd love to know where the fuel screws should be so I can have a good baseline or start. Your suggestions for the needle and mains were money. I tried my bike with the needle clip on the second notch up (4th setting?) and would hardly rev. Its definitely the clip on the bottom or richest slot.

I had almost bought a tank of yours a few months back. Well I finally have a tank all painted.. and getting it on the road. I need to take some photos for you guys.. I will get on that asap.

Naw I havent QUITE got it there yet. Its running, i need to change out the pilots and put my 530 chain and sprocket set on it, then get the brake system done and she'll be rideable. Paint still isnt done either. I got the 1100G and have spent more time riding then wrenching for once \\/

[coltrain]

Airscrews you'll have to tinker with, but as of right now i think you are WAY off base on the fuel screws.

You are correct. Its running pretty good with the pilot fuel screws out 1.5 turns. What is the stock setting? I thought I read somewhere just 1 turn out. I still need to check the plugs and mess with the air screws to iron that out.

Now with the 15 pilot jets in there the needle or mid throttle is lean. Can I put a carb needle washer or spacer in addition to the stock nylon washer thats there? I have some. It looks like I might have to find a richer needle. I'm researching the next richer size if anyone can help.

[TheCafeKid]

I think stock IS one turn out. Stock air screw is TWO turns out. Where again is your needle set? The pilots, IIRC, should really have no basis on where the needle position needs to be, but i may be wrong. If you've moved the needle all the way down to the last slot from the top and you're still a bit lean in the mid, maybe a half jump in main would be necessary. Again, my suggestions are based on suggestions i got from the carb gurus here, and as of yet I havent had mine under load or done any real chops, so I am experimenting too. How lean is it in the midrange? Generally, even a tuned pod and pipe set is going to lose just a lil there, but it shouldnt be too bad.And also, untill you've performed a vaccum sync (have you already?) its tough to judge plug chops. One or two cylinders could be pulling more vac than the others, causing varying readings in the ranges.

[coltrain]

I think stock IS one turn out. Stock air screw is TWO turns out. Where again is your needle set? The pilots, IIRC, should really have no basis on where the needle position needs to be, but i may be wrong. If you've moved the needle all the way down to the last slot from the top and you're still a bit lean in the mid, maybe a half jump in main would be necessary.

Thanks for the settings man. That helps me out as far as a baseline. I think further testing with my pilot settings will be needed before I really come to the conclusion of richer needles but yeah my needle clip is in the bottom slot and its lean at half throttle.. popping and carryin on. In my experience with workin on carbs, the pilot jet affects the rest of the circuits of mixture - Needle jets, and main jets. Makes sense because before with the 17.5 it would rock on out through the mid throttle on up to WOT, but not so at 1/8 throttle.. close but not good enough. Put the 15 pilots in and its better at 1/8 throttle but now mid throttle slightly pops and hesitates. I will let you know what I end up with but once I get the pilot sorted out I have a feeling I will be getting richer needles. I'm getting good at removal and install of carbs on the thing I tell ya.

[coltrain]

Final conclusion

Okay folks.. if your still tuned in :-)

I just got done with ironing out my bike! She runs GREAT! Ended up with using a whole nother set of fleabay carbs and they worked! I had a #4 cyl lean condition but it turned out to be the #4 carb.

I figured I would give my final settings for everybody. Maybe this will motivate thecafekid to gitr'done

Stock #15 pilot jet and I ended up with 1.5 turns out on the pilot fuel screws, and approx 1.5 turns out on the air screws. Raise the needle to the 5th setting (richest) and 127.5 - 130 main jet. Next time I have them off I'm trying out the 130 mains. Thats all folks.

[TheCafeKid]

Tell ya what, im gonna try out the 130 main first, needle in the 4th position. I'll let you know how that turns out