Dual 44 jetting help

[Bradym]

Hey y’all, it’s been a while! Used to be on here quite a bit with a different account but got out of the jetski game for years until I bought a nice gen2 the other week. Unfortunately I can’t get it to run how I want yet. It’s an 800, r&d head, b pipe, and dual 44s, blowsion flame arrestors, 170/180 compression on both cylinders. The carbs currently have 120 pilot and main jets, 2.3 needle and seat and 65 gram pop off spring.
I am able to tune the top end and get it very clean at full throttle with good plug chop readings. It revs from idle okay, but has a hesitation in the mid range before spinning up to wot. It’s not bad enough to stall the motor but it takes a second to reach full rpm. This rpm range seems to have more engine vibration too. The result is when riding it’s either full throttle or near idle, it can’t really hang out in the mid range without hesitating and then taking off. I’m really just curious if I need to change jet sizes or just keep tuning.
I see that factory pipe recommends 152.5 mains and 80 pilot jets for their pipe but that’s on stock Sxr carbs, so unsure if the bump to 44s would still work for those jet sizes or not. Thanks for any advice y’all can give! Im gonna upload a video of it running to YouTube and try to post the link here too.

 

[Bradym]

 

[Storbeck]

The jetting for the stock carbs will be completely different from the 44's, it's a completely different size and design carb.

There are two phenomenon that are common, and you might have both.

1. A hesitation, when you suddenly apply throttle and the motor acts like you momentarily hit the kill switch (not necessarily dies, just doesn't go momentarily) then catch and go strong, almost always that is due to low speed jetting a little bit too lean. Go up a size on the low speed jets and it will probably go away, then you'll have to set the high speed again. The high speed is going to have to go down in jet size about the same as you went up on the low speed but it won't necessarily be exactly the same amount of change.

2. There is also a very common situation with a good running motor with some porting and a pipe where there will be a spot in the rpm band that it does not like to run. This shows up more as a situation where you're trying to hold steady throttle, usually very low throttle just above planing speed, and the motor just won't want to hold steady rpm there, it will want to surge ahead or slow down. As far as I know there is not really anthing you can do about it other than ride around it.

The first situation can make the second situation worse.

As long as you don't go leaner on the total jetting, you won't harm anything by experimenting, especially when you're playing around with transient (suddenly applying throttle) or low speed steady jetting, very unlikely to harm things doing low throttle and sudden burst, just make sure you are not lean on long pulls of full or almost full throttle pulls. Take notes so if you don't like it you can go back to where you were. Buy a selection of jets and go try stuff, it's a good learning experience.

You'll learn more from an afternoon swapping brass on the lake than hours and hours of reading about it.

 

[Storbeck]

Actually after watching the video, that doesn't really sound like a lean hesitation. If I was guessing from the video it might be rich bog.

But, don't test like that. Go ride. It will probably act differently riding than on the trailer.

Even just twisting the screws can give you direction on rich or lean, but don't rely on the screws it's not the same affect as changing jets, especially low speed jet.

It ain't rocket science. Put a richer jet in, did i get better or worse, if it got better great, if it got worse, go the other way. If you can't tell, make a bigger change.

Also don't be afraid to play with water in the pipe and the waterbox. Usually it's a game of finding the least possible water before things get too hot, and usually it's surprising how little water you really need. Get temp strips from mcmaster.

 

[Bradym]

Actually after watching the video, that doesn't really sound like a lean hesitation. If I was guessing from the video it might be rich bog.

But, don't test like that. Go ride. It will probably act differently riding than on the trailer.

Even just twisting the screws can give you direction on rich or lean, but don't rely on the screws it's not the same affect as changing jets, especially low speed jet.

It ain't rocket science. Put a richer jet in, did i get better or worse, if it got better great, if it got worse, go the other way. If you can't tell, make a bigger change.

Also don't be afraid to play with water in the pipe and the waterbox. Usually it's a game of finding the least possible water before things get too hot, and usually it's surprising how little water you really need. Get temp strips from mcmaster.

Thanks! I was kinda leaning toward the idea of it being a touch on the rich side but was having an hard time discerning if it was a rich bog or lean miss. either way I’ll be experimenting with different jet sizes over the next couple sessions. And that’s interesting what you said about ported motors having an rpm that they don’t like as this motor has some porting according to the build list the pervious owner had for it. Either way I’m gonna first try and go a bit bigger on the low, if it gets worse then I’ll backtrack. I appreciate the information!

 

[fastgtfairlane]

2.3 n/s with a 65g spring is very low popoff. I bet your venturis are dripping fuel which is causing you to have low end response issues and once you get in the rpms, it clears out. Try raising your popoff to 20-25ish psi. 2.0n/s 95g spring should get you close. Or a 80g spring with the flame arrestors you have.

 

[Storbeck]

2.3 n/s with a 65g spring is very low popoff. I bet your venturis are dripping fuel which is causing you to have low end response issues and once you get in the rpms, it clears out. Try raising your popoff to 20-25ish psi. 2.0n/s 95g spring should get you close. Or a 80g spring with the flame arrestors you have.

This is a good point.

 

[Bradym]

2.3 n/s with a 65g spring is very low popoff. I bet your venturis are dripping fuel which is causing you to have low end response issues and once you get in the rpms, it clears out. Try raising your popoff to 20-25ish psi. 2.0n/s 95g spring should get you close. Or a 80g spring with the flame arrestors you have.

Alright I’ll add these items to the list thanks !!

 

[fastgtfairlane]

Definitely should also order some more jetsbecause there's a good chance that changing your needle and seat will flow less fuel to the jets so its likely you might need to go up on your main jet. Possibly your pilot jet too. I'd order a 115 to a 130 and 125 to 135 on the mains with all of thr sizes in between so that you can fine tune it.

 

[Bradym]

Figured I’d add a final post to this thread so those in the future can see what worked for me. After much more tinkering I still had a severe mid range hesitation that I would not tune out no matter what. Also could not get a consistent idle. So I pulled the motor to pop open the carbs…checked the stator cover vent and immediately smelled gas so I pulled the cover. About a cup of grey oily liquid poured out, turns out my front crank seal was blown completely out of the block, was shredded by the flywheel and thrown everywhere the two pieces that were left were just jiggling around behind the flywheel. Considering the fact that the motor didn’t have a crank seal in the front at all im surprised it ran as good as it did! The stator was also chewed up so I went ahead and replaced all the crank seals, installed a new stator and cleaned everything back up. Also for the carbs, I am currently running
115 pilot
125 main
95g spring
2.3 n/s
Started with each screw at 2 turns out and am just over a full turn out on them now. Still slightly rich on both high and low but I’m going to run it like this for a tank just to be safe after having the case opened up. But it runs very well now, and the low to high transition is very nice. Attached picture of what used to be the front seal and the mess that it made.