Clogging Primary Jet

[TripleKing]

For the past month, I have had an issue which feels like a clogging primary(idle) jet. If I let my 89 750 Kat sit for a few days, I get poor throttle response performance on intilal opening until I have run the bike for a good half hour. If I use every day (or every other day) there are no problems. Until the bike is used for awhile, I have to open the throttle aggressively to get smooth acceleration.

I let the bike sit for a week when I went on vacation. Yesterday, I started for the first time in about ten days. It started with the choke on on the first try. However, even when it was warmed-up, she would gradually sputter and then die, unless I gave it either choke or throttle.

I filled the tank, added a few ounces of Seafoam and rode it for about 15 minutes and the problem went away. I think I am picking up bad gas at one of two stations I visited a few weeks back. My other bikes are classics and are fueled at a station near my home and I never have issues.

Has anyone else had symptoms similar to what I describe due to poor fuel? Its this of ethanol origin? For those who use Seafoam; how often do you use it and how many ounces per tank-full do you use.

Thx!

[maniac1886]

Sounds like bad fuel is a likely cause. Idle jets are called pilot jets btw and fuel the engine below 3.5/4k. If it was clogged, it would always be clogged and wouldn't work at all. If it sets for days and doesn't start, the water in the fuel probably settled to the bottom of the tank and your carbs are sucking up shitty fuel.

[TripleKing]

Sounds like bad fuel is a likely cause. Idle jets are called pilot jets btw and fuel the engine below 3.5/4k. If it was clogged, it would always be clogged and wouldn't work at all. If it sets for days and doesn't start, the water in the fuel probably settled to the bottom of the tank and your carbs are sucking up shitty fuel.

I am at work and had a brain fart thinking of the word "pilot." Ugh! You think I could remember that after rebuilding and rejetting carbs (mainly VMs and car carbs) for 30 years. Aging is no fun.


I was thinking water as well as ethanol blended gasoline absorbs moister like a sponge, but was also considering the possibility of crud at the bottom of the tanks clogging the jet and unclogging after using Seafoam. I agree with you, water sounds more logical.

[arsenic]

If a jet and/or circuit is totally clogged, Seafoam isn't going to help in anyway. If it's just partial sediment, Seafoam might help temporarily. I still suggest a full breakdown and cleaning. I suspect sediment in your fuel tank may be a cause, but that's just a hunch.

[TripleKing]

If a jet and/or circuit is totally clogged, Seafoam isn't going to help in anyway. If it's just partial sediment, Seafoam might help temporarily. I still suggest a full breakdown and cleaning. I suspect sediment in your fuel tank may be a cause, but that's just a hunch.

Agreed. If there is something solid in the jet. A good soak and blow is required. I will ride again this evening and see how it is. I was hoping to wait until the fall to clean and re-synch. The Kat is such a pain to work on compared with my older banks. My old UJMs equipped with Mikuni VMs can be cleaned (or even rebuilt) in no time flat, including removal and reinstall.

[arsenic]

The more you work with Mikuni BST carbs, the faster you get, obviously. I can do a set super fast. Well, a lot faster than I was 100 sets ago.

[TripleKing]

The more you work with Mikuni BST carbs, the faster you get, obviously. I can do a set super fast. Well, a lot faster than I was 100 sets ago.

It is not the carbs themselves, really no more complicated than the Keihins on my old Hondas. It is the amount of bike disassembly required with the Kat. On my CB400T and my Suzuki GT380, I need only to pull the take. On my T250 and my son's CB450, I don't even need to do that.

[arsenic]

I see what you mean.

[TripleKing]

If a jet and/or circuit is totally clogged, Seafoam isn't going to help in anyway. If it's just partial sediment, Seafoam might help temporarily. I still suggest a full breakdown and cleaning. I suspect sediment in your fuel tank may be a cause, but that's just a hunch.

I added Seafoam Tuesday evening and took it for a ride. The more I rode it the better it ran. Last light, I added about 1/3rd of a bottle of NAPA fuel system cleaner (I found an unopened bottle in my workshop). It ran much better still.

I rode the bike to work today. It started up at the touch of the starter. It ran well from the get-go and only got better. By the time I got to work (35 miles/40 minutes away), the Kat was back to its old self.

I am guessing water was the problem. Either that or the "gel" problem discussed in the "ethanol" sticky in this section.

Cheers!