787 Carb Adjustments/Mods

[6KJR]

787 Carb Adjustments/Mods - Updated

I know the 787 is quite popular, for just normal use and for racing, ect.. So Im wondering if there is any jetting/pop off settings anyone would like to share, and how they work? What their 787 Mods are, ect.

I have oil injection delete and aftermarket flame arresters. Chokes removed. What carb settings would you use for this? Im trying to fine tune mine but its getting tricky.

 

[seadooya]

2.0 n/s and black(80gram) springs. Then do plug chop.

 

[6KJR]

Any word on the jetting? Someone said to run a jet up due to the oil injection delete and FA's..

 

[6KJR]

Where have all the performance guys gone??? Stock jetting good enough for these or what? lol.

 

[6KJR]

Alright. Well I tore off the carbs. I cant find my screwdriver to take out the low speed, but to the BEST of my memory, they were ONE up from factory, being 72.5 when I bought it, and the MAG carb still has that, the rear I put in a 75. My Mains are 147s.



So it goes like this....



MAG CARB 72.5 Low - 0 Turns, 147 High 1 Turn

PTO CARB 75 Low - 1/2 Turn, 147 High 1 1/4 turn

Needle/Seat are 2.0

And its NOT a black spring, and it doesnt look like any silver color at all to me either, it almost kinda looked like brass, which I would guess is the gold spring.



Now Ive done a 3 Minute WOT Plug chop and they looked pretty good, but the low speed sucks ballzzz.. So, whats everyone think of that carb mess?

 

[daverade]

He said go up to a 2.0 n/s......With a black spring, it will make a difference

 

[93mustang97sea]

well factory low speed is 1 turn out..

 

[voodoo]

To fix the idle restore the oil injection, it is a variable rate system that has few problems except oil gel from mixing brands, this is why many who do not understand remove it.

 

[6KJR]

To fix the idle restore the oil injection, it is a variable rate system that has few problems except oil gel from mixing brands, this is why many who do not understand remove it.

The problem with that is, Ive never heard many good stories of the oil pumps lasting forever. With it gone, I always know if the engines getting gas, its getting oil. When Ive flung off my machine messing around and I keep it going and its running on its side for 5-10 seconds, I would doubt the oil would be there 100%. If I loose gas well the engine dies and fine.

I left the pump on my sled, but im always questioning its ability to do the job.

 

[6KJR]

Alright well the pop off testing results. 24 MAG, 20.5 PTO. Is this within specs? Thats the black springs. I adjusted the arms so they arent sticking up either, used the razorblade. Anything ELSE I should know about this pop off?

 

[Dr Honda]

OK... I'm not exactly sure why Seadooya had you move up to a 2.0 N/S... but we won't dwell on that. (probably because of the new flame arrestors) Since you had a 1.5 n/s in the carbs from the factory... the shiny silver spring is what should have been in it. The "Gold" coloring was probably some varnish from the fuel. (the gold springs, and a 1.5 n/s would have given you a pop-off of 55 psi)


1) Why are you running so rich on the pilot (low) jets? and why are you running differential jetting? At low speed... it's not an issue.

2) as you lower the pop-off, you are already adding fuel to the low circuit,


Knowing the above... I would go back to the stock jetting for the idle/pilot jets. They should both be 70.0. Any fine tuning from there can be done with the low needle. (set both to 1 turn out)


On the high... sure, the filters are lest restrictive, and may allow a little more air into the engine. I would go one jet larger. That would be a 145. Then set the mag needle to 0 and the PTO needle to 1/4.


Finally, I would tweak the arm on the carb with the low pop-off to get it above 22 psi.

FYI... you have WAY too much fuel for a stock engine. and honestly, when you run a RAVE engine way to rich... the exhaust temps will climb, and you can burn out your rave pistons easier.

Unlike a motorcycle, these skis weren't jetted painfully lean from the factory, and re-jetting is not normally needed. Sure... the new flame arrestors may flow a little more air... but not enough to change things too much. Normally, a small tweak to the needles is all that's needed. (and sometimes, lowering the pop-off)

 

[spx800]

since the filters don't require major jetting changes, could you put a set on and not change anything?

 

[6KJR]

Id just leave your machine stock. man its a P I T A once you start messing with stuff. Either go big and take it to the next level or stock it..

I dont know why the rich bottom end either. my plugs are always wet except WOT runs arent bad. I adjusted the other spring to get it poping off at 20psi as well.

Ive never had the stock jets for the machine, it came with one size over lows and highs. Im gonna test it out on the weekend and see if its gonna give me hassle. I left my jets where they are for now to see if new springs, equal pop offs, and adjusted float arms makes a difference. Im just about ready to burn it down.

 

[6KJR]

And I did another compression test today since everyone keep bothering me about it, even when I know its not related to my specific problem, lol, and its still fine...
MAG 157 PTO 156 psi

 

[Dr Honda]

since the filters don't require major jetting changes, could you put a set on and not change anything?

If it's only a set of filters... yes, I leave the stock jets most of the time. Most OEM flame arrestors flow more air than the stock system can handle, and is not a limiting factor. Once in a while, you will find the the vacuum signal get's messed up, and then I recommend a slight drop in the pop-off pressure if you have a stumble around 1/4 throttle... otherwise, I just open the needles a 1/4 turn.

Id just leave your machine stock. man its a P I T A once you start messing with stuff. Either go big and take it to the next level or stock it..

I don't know why the rich bottom end either. my plugs are always wet except WOT runs arent bad. I adjusted the other spring to get it poping off at 20psi as well.

Ive never had the stock jets for the machine, it came with one size over lows and highs. Im gonna test it out on the weekend and see if its gonna give me hassle. I left my jets where they are for now to see if new springs, equal pop offs, and adjusted float arms makes a difference. Im just about ready to burn it down.

Well.... if you drop your pop-off lat low, you could find that you have a bad mid stumble. Especially with the large pilot jets.

Personally, I would order new OE sized jets, install them, set the pop-off to the low side of OE spec, and start there. I bet you will find that your issues will vanish.

 

[6KJR]

Im gonna guess that your probably right. Im going out sunday weather providing to do a test, and if its still lame, Im gonna order the 70's. I always thought lower pop off meant less fuel in the low speed. From what Im reading, WRONG. I do see that it doesnt effect high speed tho.

 

[Dr Honda]

Nope... as you lower the pop-off... it's easier for the carb to lift the needle, but there is less pressure on the back side of the diaphragm, and less pressure on the jets.

Pop-off pressure is a strange tuning tool, and for the most part... it should be left alone, and the jets should be adjusted. Also... for stable tuning (and some may disagree) I like to run the pop-off as high as I can. A properly tuned carb, with high pop-off pressure normally will give you a very crisp bottom, and very easy restarting.

FYI... my boat carbs are at 43 psi, and my Si is around 32 psi.

 

[6KJR]

Thanks for your input. It's appreciated. I try and help here best I can, but I'll be the First one to admit when I don't have a clue, and carbs aren't my strong point. My machine is a bastard to start if it's warm, and sits for about 20 minutes. If it sits for a couple hours it's fine.

I'll post back with my test results on Sunday.

 

[6KJR]

OK so I tested it today.. Its pouring rain which is a little hard on the face but whatever..

The machine runs about the same. With my adjustment of my high speed screws I got another 30-50 RPM.

I STILL have this dead spot from 36xx-45xx RPM.. Its just DEAD, like, baaabaaabadadabababaaabdabdabbabababada da da da.. WTF is causing that? NO backfires, it just sounds the same and wont gain RPM, then you hit a point in the throttle and it just runs normal again with MINOR MINOR surging..

Should I try raising pop off, or lowering jets in bottom end? Im gonna lean out the top end more too with the 147 jets. But this bottom end, Im gonna loose it.. If it was fuel injected like my car Id have it tuned in by now.. LOL..

 

[Dr Honda]

Yup... that huge mid stumble... where it won't clear out, is the WAY rich pilot jets.

The rich pilot jets will make it hard to restart hot too.

Set the carbs to these settings. (with some new spark plugs)


Pilot jet: 70
Main jet: 142.5
Low needle: 1
High MAG: 0
High PTO: 1/2
Pop-off 23-43. (i would make it around 27-30)


Run it for a few, and check the plugs. If they look light, turn up both high needles 1/4 turn. (that's all)

Also... buy new jets to make sure they haven't been drilled, or just warn out. (yes, jets open as they get old)


Oh... and from your PM... do not stretch the springs to bring up the pop-off. If you do, they will eventually drop back down, and may actually go soft. If you need to raise or lower the pop-off, change the springs. if you need just a little change... bend the pivot arm. But you can only bend it enough for a couple PSI.

 

[6KJR]

Well thanks for the heads up, thats what Ill try next order of partsssss..

Well after today I think my tuning is over for this year..

Broke my one leg, toasted the lower half on the other foot.

 

[Benchracer]

HOLY CRAP Man!!! I'm glad your OK. lloks like it could have been WAY worse

 

[daverade]

swwwwwwwweeeeeeeeeeettttttttttttt bro...were you pulling your trailer with this sled too??? so glad to see you were able to save the battery, that would have been a huge loss.......just fakin with ya glad your still able to think about the ski..(not dead), and thats a rad pic...what part of your leg gave in? and by "toasted" you wer burnt? if so sorry to hear bro, will make some narley storys for you when your older tho...is that a 1997 chevy corsica or cavalier?

 

[faded]

might want to look into fixing that body rot.


glad you're ok. get well soon.

 

[6KJR]

swwwwwwwweeeeeeeeeeettttttttttttt bro...were you pulling your trailer with this sled too??? so glad to see you were able to save the battery, that would have been a huge loss.......just fakin with ya glad your still able to think about the ski..(not dead), and thats a rad pic...what part of your leg gave in? and by "toasted" you wer burnt? if so sorry to hear bro, will make some narley storys for you when your older tho...is that a 1997 chevy corsica or cavalier?

The car was a 1991 Chevrolet Beretta. I wasnt towing.. And Im not sure why the battery is there. I sent my friends to clean out the car because I cant walk for 3-6 months and was in the hospital all week.. Nothing burned tho. Thankfully. I was out for 2 hours sitting there in the car.

I forget the names, tybia? Left lower leg bone snapped in half, and my right foot was crushed, so its getting surgery probably later this week. 8 Stitches around right eye, broken nose, I think I messed up a rib too.

Im kinda not happy that I cant finish tuning the carbs this summer on my PWC. I wanted that done and overwith once and for all..

THANKS Everyone for your support its a help forsure.