1998 130 hard to start cold

[Chuck1234]

Those big holes certainly look odd. Wish I had another motor to look at. Thought about plugging those holes, but if they are original, then they are there for a reason. Covering them would certainly increase vaccum.

One last thing you can try to confirm its a dirty carbs causing this trouble is as follows:

With the engine cold, as you have been doing, the air box removed, choke plates closed. Put your hand over the two large holes in the bottom choke plate and see if it starts or try's to start.

Closing off those two large holes in the choke plate will increase the vacuum created in the carb venturi, which may pull enough fuel through the idle/main jets to get it to fire off...maybe.

It seems a little strange it wont start, but after it gets going from priming, it runs well enough.

I still think you have a clogged circuit, but maybe just partially.

Best of luck

[Chuck1234]

I just think that a motor that runs very good at all rpm and starts very well all of the time except when cold would not have plugged passages/jets that are keeping the choke from working.
vacuum leak when cold maybe, or something else could be going on.
those large holes only in bottom choke plates make me wonder if that has something to do with this.

being i chased a fuel problem( high speed miss) with my C40 for almost a year before finding someone drilled out the main jets makes me think nothing can be ruled out when dealing with used motors that you have no idea what was done to them before you got your hands on them.

did the op check compression and timing?
He said the previous owner tried all sorts of things but failed, so no telling what all was don to this motor that had parts from other years put on it

Compression less than 4 lbs difference between all 4 jugs. Have not checked the timing.

[Chuck1234]

You have to allow for some air to travel thru the carb.

Closing it off altogether won't allow any air to flow. No low pressure in the venturi to suck fuel from the float bowl for the enriching process...

The engine is sucking, with the choke butterfly closed, its forces to suck from elsewhere, IE, the bowl and extra fuel (and obviously less air) for the cold start.


Remember the old GM Rochester Quadrajet 4 bbl and 2 bbl carbs? Cold, it had the choke butterfly, but instead of sucking from the bowl, they had an accelerator pump that squirted fuel every time you pumped the pedal. Cold, one pump closed the butterfly and shot some fuel into the cold engine and it started.


It's also the reason why many folks flooded their engines, pumping and pumping the accelerator making it worse...

Should have specified a bit more. Not completely plug, but make hole smaller. Yes, remember the quadrajets. Pretty easy to flood, but all in all pretty reliable carbs.

[99yam40]

But why just the 2 cylinders on the bottom and not the top 2.
strange

[99yam40]

The prime start enrichment system feeds all cylinders, the pick up point of the extra fuel is just on one carb

[boscoe99]

The prime start enrichment system feeds all cylinders, the pick up point of the extra fuel is just on one carb

In some models, yes. In some models, no.

If there is rhyme or reason as to what Yamaha does, and when they do it, I have not been able to figure it out. It is almost as if they have ten different engineering departments all determining for themselves how a product is to be designed. And any one engineering department does not talk to any of the other engineering departments. Each thinks his way is the best.

Stlange. Velly stlange.

[99yam40]

yes I agree very strange.
need to do some searching for picks of 130 carbs to see if the bottom one ever had those large holes in choke plates.
all of the part break downs I have seen so far do not show them. but they are drawings not pics

these just do not look right if trying to get a vacuum pulled to suck fuel, or maybe the motor is not spinning fast enough on the starter.
I had a chainsaw once that you had to shoot gas into the carb before it would start, ended up with a crankcase vacuum leak. Not pulling enough thru the carb to make the choke do any good

[boscoe99]

The lower carburetor has a different part number than does the upper carburetor. A few differences between the two carburetors are shown in the parts catalog, but as you note, not for the choke plate.

The SM does not differentiate between the choke plates either.

Need Rodnut, Sequoia or someone that has actually worked on a 130 Yamaha to tell us if the plates are indeed different. I suspect that they are. For some reason known only to Yamaha. Or maybe Mikuni or Keihin.

[Chuck1234]

Thought I would post a follow up. Took the carbs down. Found the pilot air passageways were gunked up. Cleaned carbs and put back together , no new parts. Motor cranks and runs good. Thanks to everyone for the advice.