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Discussion Starter · #1 ·
Hi everybody!

I have a problem with my sled, a Pantera -80. It’s really hard to start and after it have started it idles for quite a while but if I give it full throttle it just dies… I have to use the choke to get away or pump the gas. It runs really good on high rpm and it runs better when the engine is cold.

I have cleaned my carb three times, sprayed starting fluid all around the engine but I doesn't seam to be any air leak anywhere. My carburator looks like this -> CARB

The only adjustment I can do on that carb is to adjust screw nr 4 on the picture or switch jet. By the way, is this an air screw or a fuel screw? I have no idea how these carbs work, how is the fuel amount adjusted? I like mikuni VM better which has a nedle to adjust.

Any suggestions? I have new pistons and spark pluggs.
 

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Can you get a rebuild kit for that carb? The screw you're talking about is an air bleed and that's for low end only.
 

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Discussion Starter · #3 · (Edited)
smallengineguy said:
Can you get a rebuild kit for that carb? The screw you're talking about is an air bleed and that's for low end only.

What do you mean with “rebuild kit”? Do you mean to switch to some other carb or change jets? You know I’m a Swede and not that familiar with the English technical terms. I took me quite a while to figure out how to describe my problem in English.

In Sweden we call these carbs for “jaevla skitspjaellgasar helvete”.

Thanks for the reply!
 

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Discussion Starter · #5 ·
smallengineguy said:
Have you checked the fuel pump yet?
The fuel pump is quite new and should not be the problem. I have a transparent fuel hose and I can’t se any bubbles or so. The sled works fine if I pull the choke just before I give it throttle…
 

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void said:

“jaevla skitspjaellgasar helevete”.

Thanks for the reply!
Don't know what to say to that...:D

It can only be the fuel pump or carb. Have you tried a new carb? Check eBay, etc.
 

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Discussion Starter · #7 ·
smallengineguy said:
Don't know what to say to that...:D

It can only be the fuel pump or carb. Have you tried a new carb? Check eBay, etc.
What to say? We Swedes are a crazy bunch! :D

Back to topic, do I have the right carb? I can’t find any information about the carb on a pantera -80 but both -79 and -81 have Mikuni VM?

Could it be the fuel pump even if it runs when I give it choke? The choke and the main jet are on the same level in the float chamber.
 

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That is a Mikuni butterfly throttle carburator. B-40. Not very common. The screw (#4) is a fuel screw. Turn in to lean mixture, out to enrich.

Normally I would say that your carb settings are set to lean if it "bogs" when giving it throttle. However you also say that it runs better cold than hot. Often this indicates failing ignition parts. You could try reducing the sparkplug gap to .3mm and see what happens.
 

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Discussion Starter · #9 ·
palmrose2 said:
That is a Mikuni butterfly throttle carburator. B-40. Not very common. The screw (#4) is a fuel screw. Turn in to lean mixture, out to enrich.

Normally I would say that your carb settings are set to lean if it "bogs" when giving it throttle. However you also say that it runs better cold than hot. Often this indicates failing ignition parts. You could try reducing the sparkplug gap to .3mm and see what happens.
Thanks for the info about the carb however I wonder if this is the right carb for a Pantera -80?

I’ll try that spark plug trick this weekend. But is it possible that it's an ignition problem when the sled runs well if I give it a little bit choke on low rpm?
 

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Acording to the manual I have covering this sled, 1980 is the only year AC used this carb.

Now that I've thought about it some more I seem to recall many years ago an uncle I have had a Spirit powered Panther that would only run well while cold. He ended up curing the problem by replacing the center crankshaft seal. It seems that it sealed OK while cold but once the metal warmed and changed tolerances it would leak enough between the two sides of the case so as to affect the pulse of engine vacumn to the fuel pump. Heck, mabey it was a Kawasaki engine.

The only reason I mention the ignition system is because electricity likes the cold more than the hot. My 72 ElTigre drove me crazy. It ran great cold but would fall on its face once it warmed up good. I put a lot of time into checking carbs, seals, rings, and fuel pumps before finally discovering that I lost spark only when warm.
 

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Discussion Starter · #11 ·
I have actually thought of this as a possible cause for my problems. But I really hoped that it wasn’t a crankshaft seal that had gone bad. It sucks to have to disassemble the whole engine.

But once again it seams to be enough fuel in the float chamber as it runs well with the choke. But on the other hand perhaps the fuel is just pumped between the cylinders?

This crazy carb can also be found on JAG 79-81 according to www.brownsleisureworld.com, but off course is all info about the -80 Pantera missing.
 

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void said:
But on the other hand perhaps the fuel is just pumped between the cylinders?

It's not that fuel is pumped between the cyls., It's that the center seal may leak vacumn between the cyls.
The vacumn pulse is used to pump the fuel. One side of the case has vacumn while the other side has pressure. When the center seal leaks the case halves have less pressure to charge the cyl. with air/fuel and less vac to pump fuel to the carbs.
 

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80 pantera

The carb is actually a very good unit. I have the same sled with the 500 fan in it. I found that the spark plugs were breaking down when warm. You should be running the NGK BR9ES. As for the carb settings, depending on your altitude, set the low speed setting at 3/4 turn out to start with and adjust as needed to get best results. Set the highspeed jet to 1 1/2 turns out, adjust in 1/4 turn increments as needed.

If this does not help then you may need to check compression. when it is cold you may have good compression ,but after it warms up you do not, due to metal expansion. first check the torque on the heads and procede from there.
 

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Discussion Starter · #14 ·
Re: 80 pantera

RJ Gleason said:
The carb is actually a very good unit. I have the same sled with the 500 fan in it. I found that the spark plugs were breaking down when warm. You should be running the NGK BR9ES. As for the carb settings, depending on your altitude, set the low speed setting at 3/4 turn out to start with and adjust as needed to get best results. Set the highspeed jet to 1 1/2 turns out, adjust in 1/4 turn increments as needed.

If this does not help then you may need to check compression. when it is cold you may have good compression ,but after it warms up you do not, due to metal expansion. first check the torque on the heads and procede from there.
I'm running the BR9ES plugs...

Is the high speed jet adjustable? Where do i find it in this picture? CARB Nr 4 is the low speed jet, right?

Thanks for the reply...
 

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Did you totally disassemble the carb to clean it?The main jet and tube pull out thru the top if the carb. They can be finicky, you have to make sure evey little part is extemely clean.
 

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Discussion Starter · #16 ·
kingmort said:
Did you totally disassemble the carb to clean it?The main jet and tube pull out thru the top if the carb. They can be finicky, you have to make sure evey little part is extemely clean.
Yes I totally disassembled it three times to get it perfectly clean. I also pulled out the tube and checked the o-rings. The sled still bogged at low rpm.

Now I have got rid of that good-for-nothing carb and mounted a Mikuni VM36, damn the sled runs fine! It’s really strong at low rpm as well on high rpm.

I have never liked those butterfly carbs, it seams like they aren’t that good on low rpm:s. However, probably there was something wrong with this particular carb because the sled can’t have run this bad since it was new…

Thanks for all replies!

Cheers!
 
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