80 SRX carb swap

4

4strokesmoke

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Joined
Dec 16, 2011
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Age
43
Location
Buffalo NY
Id like to rid of some low end bog on my 80 SRX and I'm thinking of swapping out the old butterfly carbs for some Mikuni round slide vm38-21 carbs. My questions are would this be a good swap for a performance gain or is there a better carb I should go with and where can I find a throttle cable reference that will work since the butterfly uses a single cable!
Any help would be great!
 

I converted my 1981 440 SRX carbs to two Polaris 650 VM38mm Carbs that I bored to 39.5mm.
These carbs had no power jets, 247 series needle jets, main jets pointing down in the bowls, and had very deep float bowls. I also added weighted float drain plugs. Any engine reliability problems on my 1981 SRX ended when I did the carb conversion. My theory was the carbs were foaming the fuel with the stock carbs causing erratic lean conditions.
I don't own this sled anymore but it is still reliably running strong and used for snow drags.
 
4strokesmoke said:
Id like to rid of some low end bog on my 80 SRX and I'm thinking of swapping out the old butterfly carbs for some Mikuni round slide vm38-21 carbs. My questions are would this be a good swap for a performance gain or is there a better carb I should go with and where can I find a throttle cable reference that will work since the butterfly uses a single cable!
Any help would be great!
Click to expand...
I did this for a friend. The 79's were round slides, so just use all the specs and cables from one of those. Run quality improved a lot.
 
Another consideration when going to earlier round side carbs and jetting is the 80 was the first year that Yamaha used oil injection on the SRXs. The 1979 and earlier SRXs were specified 16:1 premix.
I eliminated the oil injection on my 1981 SRX when I installed the Mikuni VM38s
 
sideshowBob said:
Another consideration when going to earlier round side carbs and jetting is the 80 was the first year that Yamaha used oil injection on the SRXs. The 1979 and earlier SRXs were specified 16:1 premix.
I eliminated the oil injection on my 1981 SRX when I installed the Mikuni VM38s
Click to expand...
I plan on deleting the oil injection as well.
 
So I got lucky and found some OEM 1979 srx 440 throttle cables on eBay and the correct carb caps at a snowmobile graveyard off a 87 exciter 570 all for under 100 bucks. only issue now is mounting the large fuel pump makes contact with the carbs when mounted on the airbox. But runs much better now !
 
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