HX with Westcoast head, 44's, twin pipes, etc...JETTING???

[TurboLs1]

Hey all, just got my 1996 HX running and in the water. It has a Westcoast head (160psi compression), dual redtop 44's (I believe their 44's but dont know how to verify), twin pipes (not sure what they are from, but they have been modified), MSD box, R&D intake manifold, etc.

I rebuilt the carbs and observed 20psi pop-off pressure on both carbs, and jetting was 95/135 and 107.5/135 with low speed adjustment at 2 & 1/4 turns out and high speed at 1/8 turn out.

The ski runs like garbage. It will idle in the water for about 30 seconds and then die, and requires using the primer to get it started again. It runs great midrange, but bogs out and dies if you attempt anything over half throttle. Sometimes I feel the high jets kick in for a second or two before the bog out. The bogging is worse with the flame arrestors on.

I attempted to open the high speed adjustments to 1 full turn out and it seemed to come alive a little better top end for a second or two before bogging out again.

Im not sure if it isnt getting enough fuel to the carbs, or if the high/low speed adjustments are off, or if it might need a rejetting?

Any suggestions are greatly appreciated, thanks!

 

[Dr Honda]

The first problem is... if you didn't build the engine, there could be a bunch of internal mods, and that would lead to a bunch of variables in the tuning.

Here are just some thoughts to help lead you in the right direction.

1) there is no reason to have differential pilot jetting. They should be the same.

2) 20 psi pop-off is low... but those are big carbs. They may be too big for a 720 engine. The original carbs were 38's with a small venturi, and a 720 will run great on a single 44. Also, the pop-off is only half the story... what size is the needle and seat?

3) when I am jetting anything that is running bad, and I didn't do the original work on the engine... I return to stock jetting just to see what it runs like. (75;130;1.2n/s;36-60psi;1.5 low;0 high)

4) the twin pipes are probably dri pipes from Factory pipe. They really aren't for recreational use. They run VERY hot, and the HX is a small hull.


OK... I know you said you rebuild the carbs... but I would go thought them again, and verify that every passage is open, and perfectly clear.

If this was my ski... and I was not racing it (only)... I would find a set of stock 800 carbs (40 mm) and a single wet pipe, and then sell the parts you take off. There are a lot of mods that racers will do for just a couple MPH up top, that will kill reliability, and ridabillity for recreation use.

 

[Dr Honda]

Last thing... what kind of flame arrestor is it? I think you will have a better chance tuning with a factory airbox.

Just a thought... the reason it runs worse with the flame arrestor on is because the pilots are too big, and the pop-off is too low.


And finally... never try to tune without a flame arrestor. You have to run it, and it effects the tunning too much to try to tune without it.


On a side note... I've seen "TurboLs1" on other boards. Do you use that name on other boards?

 

[TurboLs1]

Tony, thanks for the info. Yes I go by TurboLs1 on all the boards I venture to, although that was a long time ago. I currently have a turbo Mustang Cobra.

Back to the HX, I have 2.5 needle and seats, and the flame arrestors are just cone filters as the carbs have the redtop velocity stacks. BTW, I had someone else tell me they think the carbs may be dual 38's, but I dont know how to verify either way?

As far as the ski goes, it's just for playing hard on the lake behind my house. I have a few other skis I use for recreational riding, so I want this one to be a screamer.

 

[Dr Honda]

ok... a set of 38's would be better for a 720 engine.

A 2.5 is a monster N/S, and will make tuning impossible. I would go back to specs above, but I would drop the pop-off to 30 ~ 32 psi, and leave the 135 mains.

Just an fyi... a 2.5 will flow more fuel than the carb internals can. I believe Mikuni made it for alcohol based fuels.

 

[TurboLs1]

Thanks again Tony, will get some jets and report back in a few days.

 

[Dr Honda]

Since you are ordering jets... I would get a couple 137.5 and 140 mains. Since I don't have an exact make on your pipes, and since your rev limiter is probably higher than stock (with the MSD) you will probably need more fuel up top. But, the 135's are a good place to start.

 

[TurboLs1]

Here are a few pics

 

[Dr Honda]

Well.... that answers that. Those are the "Factory Pipe" twins. You could give them a call to see what the recommended jetting was... but on the new pipe, they call for a 140 main.

I think the new "Spec 2" wet pipe made more power than the old twins, so they have been discontinued.

Since we don't know the CC's of the cyl head domes... make sure you run premium fuel.

 

[TurboLs1]

The 135 jets are the small / low speed jets in my carbs, is this backwards? I ordered 85 "pilot" jets from the dealer and they are the small ones, which will replace my 135's? My question is, is the small jet supposed to be the 75 and the large jet supposed to be the 130 from the factory?

 

[TurboLs1]

I installed 1.5 needles and seats tonight and installed new springs to bring the popoff up to 35psi. I left the jetting alone for now until I test it. Hopefully I can find time tomorrow and will be back with an update. Just trying a different setup in an attempt to find a tuning starting point. Hard to start from this when it wont even rev up in the water.

 

[TurboLs1]

Tested the ski today. It ran even worse than before, though im not being hard on it, just slowly applying throttle to see how it runs. It wouldnt rev up as much as before. Next plan of action is to bring the pop-off back down to 20psi with the new needle and seats, then test again.

 

[TurboLs1]

I think I may have found something...as mentioned earlier, my low speed jets are 135's and my high speed jets are 95 and 107.5. After some research, I believe this is backwards? I am wondering if the previous owner ever even had these carbs tuned?

 

[Dr Honda]

Yes... that is backwards.

 

[TurboLs1]

Okay, finally got a day to work on the ski. Pulled the plugs and noticed one had run too lean and part of the electrode was burned away. I installed new plugs and ran a compression check, still 155 and 160. I re-installed the 2.5 needle and seats, and brought the popoff back down to 20 psi. I installed 115 main jets and left the 135 pilots in. I turned the low speed adjuster to 2.5 turns out and the highs to 1 turn out. The ski started right up and idled great and actually felt responsive on the bottom. I put it in the water and it ran great bottom end and idled good. The only difference in this setup and what I started with originally is the 115 mains (original setup was 95 and 107.5 mains).

I came back in and pulled the plugs and they looked lean. I pulled the 115 mains and installed a set of 120's. I also turned the low speed adjuster out 3 turns and the high speed out 3 turns as well. The ski ran the best it has with some real power from an idle to about 3/4 throttle. A full throttle pull resulted in it leaning out and I let off. I shut it down as soon as I felt it start to bog as it leaned out and pulled it to shore with another ski. I pulled the plugs again and still running lean.

Plan is to get some 135 mains and start tuning again next day I get a chance.

 

[Dr Honda]

Past 2 ~2 1/2 turns... the needle doesn't do much, and a 120 main is WAY too lean.

If you melted the center electrode of the spark plug, I bet the top of the piston looks the same. I would pull the head and check.

 

[TurboLs1]

Thanks for the response again Tony, I have been talking to some racers that run these red top carbs, and they informed me that they do indeed run smaller mains than factory, but run huge pilots, hence my 135 pilot jets. The racers seem to focus on total jetting (pilot+main) when tuning since you are running on both the pilot and main at wide open throttle, and every racer I have consulted told me I should be around 250 to 260 total jetting (im currently at 255 with my 135 pilot and 120 main, and im still too lean). Will update again once I get some more jets.