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91 dr350

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My son has recently bought himself a 91 dr 350 straight dirt bike with a big bore kit. We're told its told a 440. The bike has carb issues 

its jetted at 160 currently and plug shows slightly rich but not horribly. We are running premium fuel treated to 108 octane.

Piston is a high compression but not sure how high. presuming around 10-11/1. at higher speeds it just seams like its not getting enough fuel and does lean back fire out the exhaust at times hot.  The bike will start ok although hard. Idle 

at times hangs. I've confirmed the float is loose on its pivot bracket. It is a 33mm mikuni pumper. My question is.. should I overhaul 

the carb or upgrade to a new 35mm? I'm waiting on my local suzuki dealer to call me back with prices on overhaul kit, float, needle and seat, and a new carb. I would just like some educated opinions on this before I proceed or try purchase anything online.  Also I have had one person tell me they've known some carbs to develop cracks, which I've seen on other older carbs but cant confirm on this one. Any help would be appreciated! Thanks all

 

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I have the same bike, minus the big bore. Same carb... I put in new jets with an overhaul. Why are u running such high octane? I'm just curious, I don't know? I run 93, my carb is dialed in, and the bike starts and runs super mint. I've torn into the motor, so if you have any questions, I'll be happy to help. Been workin on my own bikes for 20 years

Don't let Monday ruin your Sunday!

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Just to see if it helped. I've worked on cars for 20 yrs. I am a little out of my element here. Any performance engine I've built for racing I always ran race fuel. Figured worst I'd do would waist some money.

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Just to see if it helped. I've worked on cars for 20 yrs. I am a little out of my element here. Any performance engine I've built for racing I always ran race fuel. Figured worst I'd do would waist some money.

"fr0m what i see, most of the big bore kits are 440. They use a stock drz400 piston, boreand sleve the cylinder. With the longer stroke of the dr350 a 440 results. Also the end compression ratio is 12:1. I beleive this is where the power really comes from. I however do not like this point. DR350's are 9:1 machines. I will practiclly run on horse piss. Maybe machine a little off the dome or stack a couple of gaskets to drop the compression."
__________________>>>from ADV rider.  If its twelve to one, you definitely need the high octane.  Other than that I am of no help

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1 other question how do i know what model of carb I have. I know its a 33mm pumper but from what I can remember there was no model #s or letters on it.

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1 other question how do i know what model of carb I have. I know its a 33mm pumper but from what I can remember there was no model #s or letters on it.

if you look at the parts fiche, there is little difference between all years. only visible difference i could find is the 2 vent nipples point up on 90-93 and down on all others

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