Shift point

Timing is set to 38 degrees, plugs were a little brown last time I changed them

OK sounds like everything is normal mechanically.

I would like to know who you are comparing with at the track? Specifically what do they run for induction? (Lectrons/EFI/Mikuni)

You can't compare a fixed jet carb like your running to a Lectron or EFI. A fixed jet induction system will always slow down on a hot day as it can't self compensate for air temperature or humidity changes.
 

Injected now you got me thinking, i might be the only bike running "regular carbs". Thank you for pointing that out....

After going thru all your setup I think your doing everything right to get the most out of what your running.

Injected ,
Do you think it would be benefical for me to switch to Lectrons ? I'm running RS34 flatslides smallest I've Lectrons is 38 mm is that too big?

Southpaw wrote:

Injected ,
Do you think it would be benefical for me to switch to Lectrons ? I'm running RS34 flatslides smallest I've Lectrons is 38 mm is that too big?



 

Yes I do, especially since your in the Great Lakes area (like me) where its very humid in the Summer.

Once you set those Lectrons up you never have to touch them (hardly ever) My used 40's (on 1327cc) came with the wrong metering rods so my cylinder head guy sorted me out with some used rods off Paul Gast's old pro stock bike  

The small cc engine is the main issue, as most used sets out there are 38mm and bigger (OK for +1260cc) Generally if its a blistering day the larger carbs do better, the rule of thumb is at least as big as the intake valve with +2mm maximum as long as you have some CC's behind it.

I have another pic of that 1075 yellow drag bike I bought as a roller from that guy, he was using 32mm dirt bike Lectrons.
I never did get the full specs on his engine and the majority of the stats came off his Craig's List add. He probably had a big valved pro ported Z1 head (round end cam cover) 31/37 valves with some +.430" lift cams. He tried to sell me the engine when I showed up for the roller, but he wanted $3K for the engine/carbs (back in 2012) but I thought that was too much.

 

Sorry about the low res crap pic.

Maybe you can search around for some used dirt bike carbs for the 1075 engine? Either that or just bump up to a big block to be able to run larger carbs.

I am also not sure if your kick/button/cart starting (pic reminded me)

Again I am not convinced that bigger engines are more consistent, especially in points series bracket racing.
 

Injected wrote:

Again I am not convinced that bigger engines are more consistent, especially in points series bracket racing.

 

Have to agree with Injected, 100%.  

Here's a thought for Southpaw - instead of spending more dollar$ on big bore kit, carbs, etc, why not spend a fraction of that and buy some dyno time to dial in your current combo?  If there isn't a local shop with a dyno, then spend a solid day at the track (test/tune session) and just focus on jetting changes?  I think that you're close with your current setup.  Maybe tighten up your record keeping and collect more relevant data.  Have somebody video your passes.   Without a diary of good reliable data, you're pretty much relying on "gut feel" for tuning decisions, which doesn't always lead to positive results.  Again, just a thought....

For me it was always cheaper to go to the track and work on jetting than to book a day or 1/2 a day on a Dyno. Hell, even to start my little fuel injected bike up I have to go to the track as its too obnoxious to start in my garage (neighbor called the cops!)

I have done those Dyno days early on with that little injected drag bike, and it blew a head gasket one time
Back in those days it was only $60/HR

I just checked my local Dyno rates and for $120 you get three runs with printouts. Only issue is there are no jetting changes included in that package. It probably takes the guy 1/2-3/4 HR to get that done so they are making pretty good $$. Booking a day would be really expensive.

When I was running gasoline and a set of flat slides the tuneup would go away just around lunch time then come back when it started to cloud over/cool down. Its just part of the carb game, if you have small hands you can change mains easy enough track side, but its pretty time consuming.

I have the same issue with mechanical fuel injection, so you just need to pick a tuneup and stay with it until you see its slowing down. You need to remember I am only ever doing Test N Tune days, just playing around, and only ever raced whoever was in the other lane. I don't really consider that racing.

I know I need to do a better job of record keeping for sure. . Would a wide band O2 sensor be a worth while invest ? I have a data logger already it just records RPM and Voltage. $275 to add a O2 Sensor to it. Or would spending that money for Dyno time be better??

wrote:

I know I need to do a better job of record keeping for sure. . Would a wide band O2 sensor be a worth while invest ? I have a data logger already it just records RPM and Voltage. $275 to add a O2 Sensor to it. Or would spending that money for Dyno time be better??




 

My opinion on Dyno time is your at the mercy of the operator and the personality that comes with them, some are good and some are horrible.

I believe a O2 sensor and data logger are the way to go, investing in equipment is always better than renting time. With a data logger you can make your own decisions at your own pace, not so true when your on someone else's Dyno.

If you really want to go full monty then include some EGT probes on every head pipe, the more data the better.

MPS racing is a good source for all the stuff you would need, or at least will give you a better understanding of what is out there. On the web site search accessories then data acquisition.
 

SO the more i think the more questions I come up with...Thinking about closing up my piston to valve clearance to gain a little more compression. Right now piston at TDC is .001" below the deck with a .020" base gasket. The question is, is there a rule/guide line/ a limit as to how much above or below the the deck the piston can be?? Obviously not so much the ring is showing. I was thinking about getting a .010 or .005" base gasket.

I know i have alot of clearance because a .062 piece of solder doesnt get squished on the intake side and .125 piece of solder doesnt get squished on the exhaust side. Or maybe i should just leave it alone....

Southpaw wrote:

SO the more i think the more questions I come up with...Thinking about closing up my piston to valve clearance to gain a little more compression. Right now piston at TDC is .001" below the deck with a .020" base gasket. The question is, is there a rule/guide line/ a limit as to how much above or below the the deck the piston can be?? Obviously not so much the ring is showing. I was thinking about getting a .010 or .005" base gasket.

I know i have alot of clearance because a .062 piece of solder doesnt get squished on the intake side and .125 piece of solder doesnt get squished on the exhaust side. Or maybe i should just leave it alone....

 

I think that minus .001" is the most you want to be there. You always want to be negative, never flush or positive, especially if your shifting at 10-10.5K RPM.

Sounds like you may have some room with those solder measurements, but really hard to say depending on how you have your cams set.

For sure you should see if adjusting PTV with cam timing changes will give you a bump in compression. Try to get it to .050" intake and .070" exhaust minimum with at least .025" valve to valve. You could also do a Bondo mold and see if you could skim the head, you need at least .040" from the piston crown to the combustion chamber.