717 single carb with accelerator pump bog ! Switched to non accelerator carb runs gre

[Jdmcrx]

Hey guys posting for a friend

717 cleaned carb new gaskets , pop pressure set . Tried 1/2- 2 turns on the low and she still bogs. We tried the no accelerator single carb and she runs good ! Accelerator pump works too.

Any ideas ?

 

[Sportster-2001-951C-Stock]

Assuming this is a Mikuni SBN with high and low mixture adjusters only...

The low speed mixture adjustment screw is for idle mixture. You've confirmed, the accelerator system functions, the accelerator injection nozzle isn't plugged with gum/dirt and produces a strong shot as normal. Idle is good (adjust idle mixture screw, and it works fine)

Assuming you can get past the off idle dead spot and into WOT it's running reasonable, I strongly suspect your low speed bypass (AKA part throttle transition) is clogged or restricted. See the yellow colored lines of this drawing showing the path of this important and difficult to clean circuit.

Also, confirm the size of the low speed jet is the correct factory spec, depending on where/what this carb was off of originally (some other motor?) it may be too small.

And, confirm the high speed check valve isn't damaged, it should lay flat covering the hole in the kidney-shaped metering plate. It's important to use a mikuni piece in this location, not aftermarket.

 

[jondevos]

Hey. It is my seadoo he put the post up for. Thank you for the info. I had a look at the carb and the high speed check valve was not sitting flush. I took it apart and cleaned everything and now it is sitting flush. I attached a pic of before I cleaned it.

I have confirmed they are factory size jets. 167.5 main and 75 pilot.

What is the best way to clean the bypass holes? I tried using singke strands of wire but they are either too big for the hole or too weak to even push into the holes.

Machine will idle and full throttle fine. It's in between it has the issues. If I hold throttle near 1/4 throttle it will die down. If I let off or pin it it'll overcome it and work as it should. This leads me to believe the bypass holes are the real culprit. Just need to get them clean somehow.

 

[jondevos]

I've been a member here for 4 years and just now put my first post. Haha

 

[Sportster-2001-951C-Stock]

Maybe the check valve was the real problem, depending on how badly is was mangled.

May as well clean the low speed circuit while it's apart though...

1st, clean out using conventional hydrocarbon solvent and compressed air (I think you did this already, no cigar)

Then grab some phosphoric acid concentrate (coca cola isn't strong enough) and an eyedropper and use that to flush out the low speed circuit and clean out the ALO3 oxidation clogging inside those off-idle discharge ports. Remove the needle valve adjuster and the low speed jet while doing this. Then flush the acid concoction away using water and follow up with compressed air.

Have a cigar.

 

[jondevos]

Thanks again for the info. I gave it a once over and am getting good flow out of the 2 larger bypass holes now. It's hard to tell what kind of flow is coming out of the smaller one.

I will reassemble and try it like this. If still has issues I will try the acid trick. Will have to try to locate some.

 

[jondevos]

Here is a pic of the bypass holes.

 

[wfo speedracer]

Use a can of carb cleaner spray, I reccomend Berryman B12, insert the straw from the carb cleaner into the pilot jet, put on your safety glasses (do not skip this step or you will get a nice eyewash), now flip the carb upside down and hold the butterfly open, shoot the carb cleaner through the jet and observe how it flows out the bypass holes.

 

[jondevos]

It is spraying out nicely. Just installed carb on engine. Have to install pump and drive shaft and then I should be able to water test tonight

 

[Sportster-2001-951C-Stock]

Here is a pic of the bypass holes.

Yep, those are them. Let us know how it goes.

Berrymans Vitamin B12 is a good solvent, it consists of the following hydrocarbons, good for loosening gum and varnish but cannot convert native ALO3 (white death):

Component CAS RN Weight
Toluene 108-88-3 40-50%
Acetone 67-64-1 20-25%
Methanol 67-56-1 20-25%
Methyl Ethyl Ketone 78-93-3 1-5%
2-Butoxyethanol 111-76-2 1-5%
2-Propanol 67-63-0 1-5%

Here's a description of the standard acid dip, pay no attention to the chromate process as Mikuni carbs are bare Aluminum aside from the cosmetic paint.

http://oldcarblog.com/?p=15

 

[Sportster-2001-951C-Stock]

Will have to try to locate some.

Should be easy to find but I've used aluminum Pontoon phosphoric acid cleaner on the tough ones, diluted in distilled water as per directions and follow safety precautions as it's also got some hydrofluoric acid in it, very serious stuff.

ALuma Brite™

U. S. Corrosion Technologies, LLC
P. O. Box 551625
Dallas, Texas 75355-1625
(972) 271-7361 Fax: (972) 278-9721

ALuma Brite™

 

[jondevos]

Well great news. Took it down to the water and it is working great now. I now have 2 working seadoos again. I appreciate the help guys.