Engine misses after startup before warm

[James96xp]

Hi guys, excited to finally be part of the pwc club. First time I'm posting, hope you guys can help. I'm pretty good with machines, I'm a car mechanic by trade.
I bought a 96 xp in need of some love. I rebuilt the carbs. It runs pretty good but when I first start the engine, it seems to need a minute or two to warm up before it runs well. I'll try to give gas right after the start up and it feels like it misfires. I give it a minute or two to warm up and then it seems good to go. Also sometimes if I play with the throttle while I'm letting it warm up it can start to run welll as well. any ideas? Of course the spark plugs are new and gapped. Any problems with older spark plug wires? I've read some people trim them to get better spark...
I thought I'd just see what you guys had to say before I put some more time into the doo. I appreciate any insight.

 

[Dr Honda]

It's a 2 stroke. your description sounds like it's just warming up, and clearing out.

Do this.... after it's warm, and running right... Park, and kill the engine. Then pull the sparkplugs, and post a picture of them for me. Unlike a car (Especially a modern, lean running emissions car) they will be wet and dark around the threads, and rim. The electrode may be dark, but should be dry. The tip of the ceramic should be the color of a coffee bean. (Medium to very dark brown)

 

[James96xp]

Thanks for the reply doc. I'll do that next time I'm out.
I understand it's a two stroke and is different from a 4 stroke. The thing is that my brother has a 95 xp with the 720 engine and as soon as he starts his up, it's good to go!

 

[mwat65]

Your needle and seats may be leaking a little causing it to have to clear out but it’s not unusual for a Seadoo to need to warm up a bit before hitting the throttle.

 

[Dr Honda]

Your needle and seats may be leaking a little causing it to have to clear out but it’s not unusual for a Seadoo to need to warm up a bit before hitting the throttle.

Yep... exactly. OR... the high speed check valve could be leaking. In turn... when it sits... the carbs will "Bleed down". (Fuel in the regulator section drips out, and sits in the bottom of the engine) After it starts... that fuel splashes around, and eventually gets burnt out. Not a big deal.

My big Polaris does the same thing. Starts cold, and idles great. But once past the no-wake zone... as I squeeze the throttle... it will miss, and pop and stumble. But I pull it up to 2/3rd throttle, and it clears out after 3~5 seconds... and it's fine the rest of the day.

 

[James96xp]

Good to know it's not abnormal to need a bit of warm up.
When I cleaned the carbs I replaced the needle springs because they failed the pop off test. I tested them after I replaced the spring and they held the minimum stabilized pressure to spec (15psi). So I don't think they are leaking.

 

[James96xp]

What is the high speed check valve?

 

[James96xp]

Also, any ideas what I can to to help the common power surge when holding the throttle at towing speed? If I pump the throttle a couple times and I'm careful not to release throttle even a mm I can overcome it. I checked the prop and it could use some refreshing, the leading edges aren't sharp, they are a bit dinged up if I'm honest.

 

[mikidymac]

It’s the little clear plastic flap under the metering block.

Also it’s never good to just stomp on a cold engine. Let it warm up some at lower throttle settings first.

 

[mwat65]

It’s the little clear plastic flap under the metering block.

Also it’s never good to just stomp on a cold engine. Let it warm up some at lower throttle settings first.

. Definitely let it warm up. Not a problem at the lake we go to. We have about a 5 minute no wake zone to get through from the ramp .

 

[James96xp]

There's not much of a seal on the high speed check valve. If it is leaking, how would I stop it? A rebuild kit of the carbs would come with a new check valve?

 

[mikidymac]

Yes, but make sure you are only buying Genuine Mikuni parts.

 

[James96xp]

Hey dr Honda, the plugs look ok. The pto side plug is darker though.

 

[Dr Honda]

Hummmmmmmmmmmm............... The PTO is normally the lighter side.

The dark plug looks "Sooty". Not just rich. That's a sign of incomplete combustion. The lighter one looks very light. Almost too lean.

When was the last time you checked the compression?
I'm assuming these are after it's run for a little while and warmed up? If so... I would run a compression test, and I would open the MAG side high screw 1/4 turn. I would also close the PTO side high 1/8th turn. THIS IS ASSUMMING IT WAS AFTER IT WAS CLEARED OUT ! if it wasn't, then don't make any adjustments yet, and just check the compression. I'm not thinking it's bad... but there may be a spread.

 

[Dr Honda]

Here's what a healthy 800 should look like. The color of meadium to dark roast coffee beans on the ceramic. Electrodes should be dark and dry... rim and threads are normally wet with oil.

 

[James96xp]

Ya, this is after clearing it out, warmed up and running it for about 15 minutes. I did a compression test about 2-3 weeks ago, both cylinders at 137psi.
When you say the high screw you mean high speed adjustment screw? The one that only has an adjustment range of 180 degrees right? They are both set to spec right now, right in the middle. I was definitely thinking of richening the mag side and leaning out the pto side. But why adjust the high speed screw and not the low speed?

 

[mikidymac]

If you pop the plastic cap off the high speed screw you can adjust them as much as you want.

 

[James96xp]

Should I do two test runs to dial in the carbs? One where I idle and use low throttle inputs for 10 minutes in order to dial in the low speed adjustment based on spark plug appearance. Then another one where I rip around using high throttle inputs to dial in the high speed adjustment. Seems like a good technique but I'd like to know what you guys think because dr Honda suggested I only adjust the high speed screw based on the last pictures of my plugs, and I was curious why only adjust the high speed screw?

 

[Ryan727]

There's a pretty good sticky post here about carb adjustments, by Bills86. Just going from idle speeds then ripping around can miss a few things. Here's a snippet from that thread:

"1. Throttle response should be crisp, with no hesitation.

2. Ride the boat at a constant 1/4 throttle opening for about 1 minute and then quickly open the throttle fully, there should be no hesitation and the engine should not show signs of being loaded up. If it hesitates, it's lean; if it's loaded up, it's rich. "

 

[Ryan727]

It also breaks down which part of the carbs work on different throttle positions. This can help you dial in what needs to be adjusted.