Mikuni Fuel Pump Failure

[gcrisler]

Over the weekend my 582 Rotax started idling rough, she was getting too much fuel. After the morning flight I parked the machine and had lunch. I came back about 4 hours later and noticed fuel dripping out of the air filter. I turned off the fuel valve, took off the air filter and found the front carb/cylinder to be the culprit. I figured it must be the needle and seat in the carb, so I replace the carb with a spare I had laying around and went up flying again. While up in the air I noticed air bubbles in the fuel lines going from the pump to both carbs. I didn't remember seeing the bubbles before, however, I hadn't looked very hard either. I landed and the machine idled rougher than ever. I parked the machine and sure enough gas started dripping out of the front carb again. I knew the carb I just put on was good. I went in and ate dinner and while I was sitting at the table it dawned on me that a hole in the fuel pump diaphram would let the gas drain into the crankcase through the pulse line and also explain the bubbles in the fuel lines. I took the fuel pump apart and found one of the check valve retaining rubber push rivets broken and wedged up against the diaphram. Over time this had wore a small hole in the diaphram. I replaced the parts and everything was fixed.

The fuel pump was the standard Mikuni round hockey puck size unit.

I am only posting this in hopes that maybe someday it will help someone else out.

Garret Crisler

[Udi]

How many hours did the pump have, Garret?

Udi

[Chuck Irby]

Hey Garret, when you took it apart, could the gaskets be reused, or were they damaged taking it apart? I ask because there are basic repair kits with the two diaphragms and a couple of the main gaskets for under 10 bucks, and then there are some available for $69 that have everything in them. I've also seen the whole pump for under $30.

[gcrisler]

I have no idea how many hours were on the pump, it was out of an old snowmobile that I junked a few years back. I order repair kits with all of the gaskets and diaphrams for $6 from www.denniskirk.com, PN# 17-161. The complete pump is only $25, PN#16-10. it is an orginal Mikuni not a knockoff.

Garret Crisler

[Chuck Irby]

Thanks Garret, for the link to the the aftermarket parts store. Have you used many of their parts? If so, how do they compare with the OEM's?

[scottessex]

Dennis Kirk is GREAT! I have been ordering motorcycle parts from them for years. Everything from Harleys to Honda Trail 70's. I just got most of my Suzuki 530 parts from them, I had them in 3 days. Plus, if you order over $100 worth of stuff, the shipping is free, Another plus, they will usually match other peoples prices.

I have never had a bad experience with them.

[Chuck Irby]

10-4, thanks Scott, I'll give them a try.

[MMorgan]

I second the recommendation for Dennis Kirk.......I have ordered motorcycle stuff from them for years.

[joeheli]

I have always heard that is not recommendet to repare the fuel pump. Even the people that sell the repare kit has post that they don't recommend the rebuild kit. For example aircraft spruce:

http://www.aircraftspruce.com/catalog/eppages/mikunifuelpump.php

Maybe because is better for them to sell you the new pump, or maybe because of failure :eek: . What do you guys think? :confused:

[scottessex]

It is probably too easy for an inexperienced person to assemble it wrong, or damage a diapragm when rebuilding. As cheap as they are, it is good practice to replace it, if you are unsure of your mechanical skills.

[PW_Plack]

I'd bet the recommendation not to rebuild is at least in part a liability concern. End users may not be trusted to correctly evaluate the integrity of the re-used housing.