Another carb problem : I think

[jaykup]

I've got this Seca 750 and had it running after i bought it. I didnt do anything to it at that time, and it seemed to run OK except for low-end throttle, it seemed as though it was miss firing. As soon as i would give it gas, it would go just fine.

I figured it was carb related, from sitting forever, and I was right, the carbs were extremely dirty.

One of the smaller jets was clogged, and I am guessing that is what made up that low end missfire.

I cleaned out all the jets, everything. Carb cleaner, air-compresser, the works. The floats were still in adjustment (17.5MM) as I measured them all

The floats are also in good shape (did the hot water test to find leaks, nothing). I cant brake free the bottem drainage screws, but everything else was taken apart. (except the mixture screws)

Now the bike wont start. The two far cylinders (1 and 4) are firing, but the middle arnt. All are getting spark, new plugs just installed. The spark to me seems weak, but its there. the main thing is, the plugs arnt wet when im turning it over and over and over. So i thought i messed something up in the carbs.

I took them off, and all the bowls had alot of gas in them. Same amount from what I could tell. I know the jets are cleaned, just double checked them today. For a while, I had it idling, and i could rev it to around 4K or so just fine, even higher, but as soon as I tried to take off, it just died. Like it was running out of gas. Which is why i went to the floats, and the needles.

What would be causing this? What else did I miss? The thing ran great before i tore the carbs apart, so i really dont think its spark

The coils tested 20K and 30K or so, and they were supposed to be around 25K. Also all are sparking.

Where do I start? The petcock also flows great.

Jake

[YamaHead]

If you have the YICS head design (which I think you do).....you'll need that damn YICS shut-off tool to Synch those carbs! :wink: ....My '83 750 Maxim does the very same thing everytime I mess with the carbs :roll:

Problem is (@least where I live) is that getting one of those special tools is next to impossible....(the local Yamaha dealer tells me they don't make 'em anymore! :shock: I am fortunate though, as a friend of mine who lives close by, has this tool....which I currently need to borrow :oops:

It inserts in a hole on the intake side of the head, right under the carb boots....(bolt there needs to be removed first). There's basically sub-ports between the cylinders that need to be blocked off while synchronizing.....or else you'll never get it right :? I think this design was to equalize the vacuum pressure between the cylindrs, but TBH, it's a pain in the Ass! :x

I've dealt with it for quite awhile on 3 different Seca's & now this Maxim. That's why Im keeping my eye's peeled for a good used newer XJ WithOut this type of head, for a daily hack. :wink:

Did you also clean the Air Jets in the tops of the carbs?......that too can make a difference sometimes.

I'll have to do a search again & try to source one of these tools out from somwhere......Let me know if you possibly find one.....I'd be quite interested in getting one. It sure does make life alot easier when you've got the right tool for the job :wink:

Best of Luck with it

[jaykup]

Sounds good, I saw a refrence to this tool in my manual. Yes, I did clean out the air jets. I think you may be right on that too, because it only likes to fire on FULL CHOKE. I wil check the local yamaha dealership, and see if they will order me one, its worth a try. If they can, ill have em get two, if you need one Ill see how much they are first of course. But, this being sunday, I am sure they are closed.

Ill let you know soon

Yes, it is a yics, my friend with his interceptor is always like.. YICS, constantly saying it when ever he sees my bike.. :

Haha, anyway, ill let you know.

Jake