BlackJack's rarely 'come on' the high circuit, chokes etc

[Spoony]

I've got an issue that I thought was a blockage in the water box, turns out it's not.
It's a 701 SJ, 46mm BlackJack's, Riva Girdled head, R&D Wetpipe yadaya, motors (fresh.... a few times now burnt out pistons lo).


What is happening it's failing to come onto the hi speed circuit (I think) of the carbys. Inturn trying to ride it sees the pipe get too hot (lean?)
Idles fine, blips and revs fine out of the water but on the water its OK (well how it's always been) on low throttle, open it up and exhaust noise changes to some sort of weird musical instrument and ski doesn't go anyway (well holds the same speed/decelerates a little).
However sometimes it just hits like a switch and comes on, either on occasion when hitting the throttle or sometimes where throttle is already in the area where it comes 'one pipe'.

Another test that proves its fuel related is if cruise around at low throttle and pump up the carb's using the primer I can hit WOT and it takes of sweet (haha).
I've rebuilt the carbs, and had them apart since then (Piston failure). I've blown through them with pressurised air hose. I can't see anything wrong. I've set the jetting and screws up as per Art's recommendations.
On thing I noticed is there was no little filter inside the carbs originally, I used the one in the kit but perhaps Blackjacks are not suppose to ? (in saying that it did 20hrs with the filters running fine).

I'm going to pull them off again, but I'm thinking maybe there is water trapped in them or something blocking the jets? (Fuel seems OK).
It's done this on occasion before, I then may have trailered it only the next day 1hr or something, put in the water and its sweet.

I really want to avoid doing another piston, I'm already likely going to have to hellicoil some exhaust threads and head too I've had this thing apart and together that much

Cheers for any advice

 

[ryan]

if the pipe is steaming it will lean it out. sounds like you have going on. sound change is one of the give aways. it will run hard for a few sec then start to feel like its holding back. starts to lose rpms.

 

[Spoony]

I don't think it's the pipe causing it. I know it's go no water blockages (check this previously), and when it does decide to run right pipe temps are right down.

When it does 'come on' and run hard/properly it holds speed and doesn't dye off.

Signs of this issue inially were occuring out of turns. It would bog on snapping the throttle. I could hear the strange note change from the pipe, but usually it would then just hit hard and shoot off. Now it's doing this pretty much 99% of the time I give it throttle appart from the rare occation with it comes on and goes full noise.

Can't be spark etc as priming it up would have no effect on anything accept lack of fuel getting consistently dumped by the carbs

 

[ryan]

check the return for blockage? i had one with a grain of sand stuck in it. it would run good then run bad good then bad. lol

 

[Spoony]

good thinking.

It's normal NOT to be able to blow back down the return line right (pretty sure it's just a one way thing)

 

[2XLR8]

I once had a similar symptom and it turned out to be a linkage coupler that occasionally would closed the slave carb. It appeared ok even when I pushed the throttle plate with a pencil. With the vibration it would slip the set screw and the airflow would close the throttle plate under acceleration. It was always fine out of the water. The problem only happened when you rode it.

 

[masterblaster]

both of those issues above would cause a rich condition though,I dont think they would cause a piston to burn lean condition,Id start with checking the plugs after a short wot and see what they read,id check pop off in both carbs,and look real close at your fuel pump on the carb that runs the cylin that last burnt out,these diaphragms fail slowly sometimes from water inges and would cause this prob to seem to get worse and worse.they usually first show up in hard right turns when g forces are fighting against the fuel flow as well.

 

[jetski9010]

dual 46 blackjacks on a 701? What pop off are you running with that setup?

 

[Spoony]

I'm pretty sure there 46, measure 46 at the base.

Running 130 low/main jet, 115 high jet, 2.0 seat/needle, 95g spring.
1 1/8 on the lows 1/2 on the highs. Art recommened me this. Was working well.......... well when it was working lol.

I thinking it's definately a lean issue, pipe getting hot and dumping stacks of fuel via the primer indicate this. I'll check the linkage all the same, it is a bit flogged out.

Plugs have always looked consistent and good. Either putting round on the low or doing a WOT test with fresh ones.

 

[CARBONX2]

All passages clean? Use a little squeeze bottle/bulb to check flow on the different circuits

 

[2XLR8]

If it was working well before With what you had then you need to look for something causing the problem other than the jetting. If you are sure it is lean then turning the high to 1 and 1/2 should fix that problem for test purposes. I had old polyurethane fuel lines before and they can suck air at the inlet fittings of the carbs. All it takes is one carb to suck air in the fuel line to cause major problem.

 

[Nuklear6]

I def agree with the above post about it not being a jetting issue, as well as i would def check the fuel likes for any pin holes or wear marks that could possibly suck air. The next thing i would give very careful attention to is the fuel pick up, fuel shut off switch (if still running one), and the fuel tank. Superjets and yamahas in general are known for fuel shut off switches going bad and causing the pump to loose a perfet prime. If you are not running a shut off switch and are only running off the reserve pick up line i have myself had the rubber at the end of the line (bottom of tank) press against the bottom and cause fuel starvation. Easy way to fix that is to cut the bottom of the hose on a 45 so that is no longer possible.

 

[jetski9010]

I'm pretty sure there 46, measure 46 at the base.

Running 130 low/main jet, 115 high jet, 2.0 seat/needle, 95g spring.
1 1/8 on the lows 1/2 on the highs. Art recommened me this. Was working well.......... well when it was working lol.

I thinking it's definately a lean issue, pipe getting hot and dumping stacks of fuel via the primer indicate this. I'll check the linkage all the same, it is a bit flogged out.

Plugs have always looked consistent and good. Either putting round on the low or doing a WOT test with fresh ones.

That just seems like a really high pop off to me. I was running that same setup 2.0 N/S with 95g spring on a 701 with stock dual 38's. Art set up dual 44's for me for a 760 and the pop off was around 12-15 psi. If that was he is saying to run I guess thats right but just seems really high for a dual 46 blackjack setup on a 701.

 

[masterblaster]

fuel line pickup prob wouldnt start to show issues with turning first,assuming the tank was half full at least.but with the exh note changing then the issue starting,its possible you have a partial clog in your cooling leading into or out of the pipe,maybe near a T or restrictor.head Pipe drys out carbs go lean,I run my ski on a hose at low pressure and high rpm and blow compressed air short bursts into pissers after beaching rides,clears any possible restrictions out depending on how your restrictors are set up.

 

[Spoony]

Cheers for all the idea's guys.

Tonight I hopefully will get some time to look at it. I'll definately be stripping the carb's again. Previously I did blow through with hi pressure air (only when they were stripped) and made sure/felt every jet/passage was clear etc. Not that it couldn't be blocked now.

I was considering pissing off the internal fuel filters as it didn't have them previously, maybe thats some cause of restriction.

I'll just replace all the fuel lines (again) and be done with it. They have got some rub marks here and there.

Setup runs twin fuel lines with twin filters for each cab. Carb's have their own fuel pumps.

I thought about the pickup sucking on the bottom before so moved the hose up in the tank some, will recheck tho.

Obviously given there there is no fuel switch anymore.

Interesting thoughts on the pop off. I did email Art the setup and thats what he recommended.
Previously was a 2.5 seat, 120 low, 115 high, now 2.0, 130, 115. It also did have a 95g in it before so the setup isn't all that different.

I'm 99.9 sure its not a water flow issue, pisses and all jets are free. I think mentioned earlier I run clear filters on lines with jets, i can see the sand/ build up and empty them now and then. Works a charm for keeping out of the exhaust jets.

Oh issue presents even with a full tank so don't think its a pickup issue (Unless it's sucking on the bottom as suggested).

 

[Matt_E]

Is the diaphragm side of the carbs facing the exhaust hose?

 

[Spoony]

yep yep, surely is, I need to pack something in there as the screws wear out the bloody hose cause of the size of the carb's.

I did notice at a freeride event on the weekend many had the carb's the other way? Reason? Would mean modding the manifold to suit the throttle linkage etc.

 

[SUPERJET-113]

That just seems like a really high pop off to me. I was running that same setup 2.0 N/S with 95g spring on a 701 with stock dual 38's. Art set up dual 44's for me for a 760 and the pop off was around 12-15 psi. If that was he is saying to run I guess thats right but just seems really high for a dual 46 blackjack setup on a 701.

I run my pop off at 24 psi on my dual BrapJack 44's. Thats what Art recommended and they kick butt up and down the power scale.
Were those dual 44's you had Art setup OEM 760 44's or BrapJack 44's?

 

[Matt_E]

yep yep, surely is, I need to pack something in there as the screws wear out the bloody hose cause of the size of the carb's.

I did notice at a freeride event on the weekend many had the carb's the other way? Reason? Would mean modding the manifold to suit the throttle linkage etc.

It is possible that the exhaust hose is blocking the holes in the diaphragm covers intermittently. This could cause the symptoms you describe, especially in turns. (They are atmospheric pressure reference holes and essential for proper popoff operation)
You could flip the carbs around if your manifold and throttle cable allow it.
Or you could drill an additional hole into each diaphragm cover. This is what I did. (I drilled them towards the bottom of each plate).

Something to consider.

 

[Spoony]

113,
24psi is close to a 95g spring I think (should give around 26psi which was what I was recommended). We are talking more fine tuning here (ie a few psi) than outright wont go hard at all! haha

I dont' know the source of the carb's, I bought the ski with all the good bits as a bit of a wreak on a decent trailer and have rebuilt it all.

Matt,
Thats acutally a really good suggestion. I did not think of that at all. I can work around that no worries. Filpping the carbs would men modding the mainfold (R&D) so wont bother with that just yet.