800gp 46 Mikuni carbs

[Tosh]

I have a wdk weapon with a gp800 bored to a 997. Last summer my ski would bog out and die if i went from idle to half throttle if i feathered the throttle i could eventually get out of the bog and on the pipe but as soon as id let off the throttle and punch it again it would die. I tested the pop off tonight thinking that may be the issue and my pop off is 15psi and the 18psi in the Mikuni 46s. Does anyone have any idea what the pop off should be or a starting point?

 

[DylanS]

I have a wdk weapon with a gp800 bored to a 997. Last summer my ski would bog out and die if i went from idle to half throttle if i feathered the throttle i could eventually get out of the bog and on the pipe but as soon as id let off the throttle and punch it again it would die. I tested the pop off tonight thinking that may be the issue and my pop off is 15psi and the 18psi in the Mikuni 46s. Does anyone have any idea what the pop off should be or a starting point?

I always ran my 927’s between 19-26 psi. You probably have an insane amount of fuel pissing out with pop off that low and the classic 800 shake. Go to a higher pop off, start at 20-21, and if it leans it out bad bump up your low speed jet gradually. If your carbs return restrictors aren’t drilled out either your fuel pressure is for sure stupid high with that engine and that could be a large part in your issue as well.

 

[Tosh]

I always ran my 927’s between 19-26 psi. You probably have an insane amount of fuel pissing out with pop off that low and the classic 800 shake. Go to a higher pop off, start at 20-21, and if it leans it out bad bump up your low speed jet gradually. If your carbs return restrictors aren’t drilled out either your fuel pressure is for sure stupid high with that engine and that could be a large part in your issue as well.

Thanks i will try and bump it up a little and see if that works. I’m not sure if the return restrictors are drilled out or not. I’d assume they are since Jeff put the ski together but I’ll check.

 

[Tosh]

Thanks i will try and bump it up a little and see if that works. I’m not sure if the return restrictors are drilled out or not. I’d assume they are since Jeff put the ski together but I’ll check.

What size jets do you run in your carbs?

 

[Storbeck]

The symptoms you're describing sound more like lean than rich. Increasing pop off will make it leaner. It's possible to have more than one problem at a time so resetting pop off and basically jetting the thing as if you're starting from scratch I'd not necessarily a bad idea, but I would make sure you don't have another problem. What you're describing would be a classic symptom of dirty carbs especially the low speed jet and the low speed progression holes in the side of the carb. All of that must be perfectly clean and you need to KNOW it's perfectly clean before you can try to diagnose or tune anything else.

 

[Tosh]

The symptoms you're describing sound more like lean than rich. Increasing pop off will make it leaner. It's possible to have more than one problem at a time so resetting pop off and basically jetting the thing as if you're starting from scratch I'd not necessarily a bad idea, but I would make sure you don't have another problem. What you're describing would be a classic symptom of dirty carbs especially the low speed jet and the low speed progression holes in the side of the carb. All of that must be perfectly clean and you need to KNOW it's perfectly clean before you can try to diagnose or tune anything else.

It’s possible it’s lean but the reason i think it’s on the fatter side is my pistons are black with carbon build up and the pipe out the back of the ski is constantly spewing black sludge like it’s running fat. I don’t know i could be wrong though

 

[Storbeck]

Lack of piston wash is an indication of lean jetting, shiny pistons with no carbon would indicate very rich.

But, you are describing symptoms of lean at low throttle settings, it's entirely possible (maybe even common) to be lean at low throttle settings and rich at wide open throttle.

When you have a situation where opening the throttle suddenly make the engine hesitate or die, but opening slowly doesn't, or at least isn't as bad, that's classic indication of low speed jetting too lean (really low throttle jetting would be a more accurate term, but people say low speed)

What happens is, if you are tooling along at just off idle or low throttle and your mixture is good enough to run but a little on the lean side, you open up the throttle quickly and suddenly there is a bunch more air, but the fuel takes longer to get there, so momentarily it's too lean to run, engine dies, or at least hesitates.

If the progression holes are plugged, you can get weird situation where one specific throttle opening it will run but then you open the throttle past the next progression hole and it won't, it will be weird, but in general, lean on the low speed.

Making sure your carbs are good and clean is easy and free. Just do it. Make sure those progression holes are clean.

 

[DylanS]

Was it running good prior to this on the same carb settings? Odds are if it was and nothing changed than you’re just lean with dirty carbs. If you didn’t have your specs written down and just checked now then it’s less clear. When you say “15 and then 18” do you mean your 3psi off between carbs?
My jetting will be different than yours but for reference I ran roughly 21psi 115 low 120 high on my 48’s on a 927 in pa but will be worlds off from you I bet.
It’s easy to mix up a super rich condition off the bottom and a lean condition. Most times it’s lean but I’ve seen it where it’s rich a few times as well. A very rich condition involving raw fuel spewing out of your carbs will almost always rear its head when you let almost entirely off the throttle after a WOT pull and go to get back on the throttle dumping a load of raw fuel into your engine. Ride around for a minute barely on the throttle and hammer it. If it dies on you it’s lean and if it blubbers and pulls thru it’s rich.