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Discussion Starter · #1 ·
Hi all,
bought a 1985 gsxr750 which had a dead patch above 6000 rpm, the local bike shop has sent lots of time (and my cash), fitted standard jets, needles etc and it still not right.
Do pod filters muck up the top end performance?

be kind to me as this is my first post on this forum


Cheers
Pete.
 

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They will mos def make it trickier to jet perfectly. Pod filters can be super finicky.
There has been a raging debate for centuries as to which is better.
If you just wanna set it and forget it, stock airbox with a K&N is the way to go.
If you insist on the absolute best performance, and are willing to do the work necessary, Pods will usually flow just a tad better. The later the bike, the less gain you get though, as manufacturers got better and better with tuning airbox resonance and pressurizing the box with ram air.
On the old 85 the general consensus seems to be that the airbox wasn't that great yet, and there were gains to be had. Expect to work on them alot to get them to where you are happy with them.
The shop that was doing your tuning, were they doing it on a dyno? If not, take it to a shop that can.
Or find an open, straight, lonely piece of road and get REAL good at doing plug chops and reading the plugs.
 

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Pete,
I wonder what bike you are comparing the gixxer to when you talk about the flat spot. If it's not a hard stumble (rich), I would say that it is probably just the profile of the cams, rather than a jetting problem. These bikes are made to make power at the top end (particularly with K&Ns and a pipe), at the expense of some low/midrange. I spent months trying to jet a flat spot (at the same rpm) out of an old Kaw. GPZ750, before finally learning that it was the cam profile rather than the jetting. My 86 750 hits a flat spot at 6k just before the power comes on at 7k. Mine's got big carbs on it, which probably makes it a little worse. But it feels normal to me. Just keep it above 7k when you need power.
Hope this helps.
 

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i just finished jetting a set of those old flatslides on an 85. the 29mm ones. stock jetting is 97.5 i think from memory. we ended up with some old 124's in it. i had them laying around so we stuck them in to see if it cleaned up the top end. soon as we did it went like a scolded cat all the way from idle to rev limiter. it had pod filters and an exhaust.
so keep experimenting, youll get it eventually!!
 

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Discussion Starter · #5 ·
Thanks guys, very helpfull, the shop is still working on it, they taped an exhuast gas thingy to it and took it for a run, its rich at low revs (less than 6k) & lean at higher revs.
Looks like my $2000NZ bike is becoming a $3000NZ one?
Cheers
Pete.
 

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From Oldskool Suzuki the following info might suggest an answer. I had an '86 and there were times that my wife had to take my .45 from me. I was gonna shoot the bitch. It was so shitty to jet so that it worked even halfway decently. Good luck. Troy341

1985-1987: F,G & H models

"The carbs will be fucked if you buy one of these, guaranteed. In fact, check that the engine is basically sound on these older models before doing any tuning. For the early GSX-R750s, use 750J/K carbs from a breaker. They're 36mm and the best GSX-R carbs ever made."

"Whether you're using the original 29mm carbs or a set of 36mm CVs, run a Stage 3 Dynojet kit with individual twin filters. You have to go to Stage 3 with the bigger carbs anyway because the venturis are too big for the old airbox."

"Early GSX-Rs respond very well to a decent quality pipe. You want a 4-2-1 system, and Micron still does a fitment. Hindle also does a full system which works very well, but it's mild steel so needs to be looked after. You could even try retro-fitting the original exhaust system from a 750L with a slip-on can and that should work well when set up properly. All of the GSX-Rs need dyno time to make them work well. You can just bolt stuff on, but it'll never give the best results."

"With the pipe on and the Stage 3 jet kit with 36mm carbs, you're looking at a 10-12% power increase (94bhp) at peak, and a much livelier mid-range. All GSX-Rs eat coils, so on early ones they definitely need checking or replacing. It's also the only bike ever made that needed an ignition advancer. The standard ignition is pretty woolly and an adjustable Simms & Rohm item will fill in the mid-range and give you better throttle response right across the rev-range."

"Handling? 750J rear wheel goes straight in, as will the front end from any of the GSX-R series. The steering bearings are identical on all models, so there's no reason why you shouldn't stick in upside-downers if you like. The standard 750F/G wheels are so weak that you can flex the spokes with your hand. Best to change them, I think. A 17mm master cylinder (1000 Exup) for the brakes will transform the standard brakes and use SBS-RQ pads for maximum breaking."
 

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Discussion Starter · #8 ·
Hi All, Problem found, inlet cam had jumped a tooth on the chain, so all that work rejetting (by the shop) was a total waste of time (and my cash).

Should be ready for a test flight Monday (sorry thats sunday for you lads in the US)

Cheer Pete
 
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