Bllet proof 760 ? ? ?

[shepster]

Hi guys, have a freeride ported 760 61X motor running a single ATP 48mm carb, ADA head with 35cc domes squish is .45- 185psi , MSD enhancher, factory b pipe, solas 13/17 impeller, dual cooling. Running 50/50 pump & av gas
The problem is this is already on its second bore as it keeps picking up on the bores. Caused by detonation
Could anyone help out with set up to make this more reliable, dont mind going to pump gas only just want to ride without the hassle.

Many thanks

James

 

[SuperJETT]

Detonation is caused by too much of any combination of timing, tuning, heat.

Do you make full throttle runs? A single works great except for wot runs. I had a single Novi 48 with external fuel pump at one point and even after taking the main jet OUT of the carb, it still wouldn't richen up on wot runs. It had great power, but wasn't safe to run wot.

 

[shepster]

Hey, yea sure its to do with that as only happens when i get abit carried away. The carb is running 120 pilot and 180 main jets.
Just after a sollution to stop this from happening if i lend the ski to someone other than me. I have learnt my lesson the expensive way.

thanks
james

 

[shepster]

Did you swap to 62t cases in the end ?

 

[SuperJETT]

That was on my 62t 701, total loss, Speedwerx freestyle pipe, ported, pump gas.

Even with Mikuni's biggest pump and the main jet completely out of the carb, it still leaned out on wot runs.

Now, I know on that Novi the fuel path is different inside, it takes a longer path to get to the high speed circuit, so that probably affects it some. It makes the carb more sensitive, but probably limits it's max fuel flow.

I had plenty of fuel pressure and flow on the pump side, but it just couldn't get it into the carb throat.

Unfortunately, I don't think you'll be able to make it 'safe' at wot runs with a single.

I now have dual 44's.

 

[SkiDaddy]

Compression may be a tad high for extended WOT runs as well.

Do you have any initial advance?

 

[shepster]

Hi compression was recomended by Jr for best performance, mabe not wot. The timing is still on the stock marks with just the enhancer, limit set to 8000

 

[waxhead]

it all sounds ok to me other than that single carb
put twins on there dial them in and hang on

 

[sjetrider]

Twin 46 or 48mm carbs for WOT bro. your single carb setup is perfect for reliable freeride but not for wao runs. Dual carb mnflds ar cheap for the 61X but carbs will run you a few $$$$. I have a simular setup in the square below and would not recomend long wao stretches at all on it. At 185 comp you should be fine w/ pump gas. Just curious how this motor was ported (obviously not at all or for freestyle) as 35cc domes will not make 185psi if exhaust ports are raised at all. If you want top end, raise the exhaust ports 1mm or so and this may help solve your issue as well.

 

[shepster]

Hi the porting was done by Group K as part of their 760 BBK, for freeride. Compression was originally 165 with 38cc domes but Paul suggested fitting 35cc domes to bump things up.
Are twin carb 61x manifolds still available or would i be better swapping to 62t cases, probally the better option for the future ?

 

[SUPERTUNE]

Is this in a Waveblaster? Keep the compression by getting a 62t stator and flywheel and let me set you up with an Advent CDI! You need to have the timing retard back to about 16-17 degrees at any rpms after about 6200 RPM/s. If you don't, then you need compression back down for WOT running. Also what is your set-up on the pipe? What's the headpipe size? Have you bored it out for the big bore motor? (see Harry's update on the 'B' headpipe for this) If not start there... PM for more info regarding this. The other thing would be to lower the squish ratio also as you probably are up about 50%. You need to measure to know for sure.
I don't think your single carb is the sole problem as you stated your running a 50/50/ mix on av gas and that helps a lot.

 

[FL-cracker]

^^^^ Do what Chucky says.

If you want the best performance from that motor, I would strongly suggest switching to 62t cases + dual carbs.

 

[shepster]

Many thanks guys, Chuck you have mail :biggthumpup:

 

[RMBC Freeride]

At 185 comp you should be fine w/ pump gas. Just curious how this motor was ported (obviously not at all or for freestyle) as 35cc domes will not make 185psi if exhaust ports are raised at all. If you want top end, raise the exhaust ports 1mm or so and this may help solve your issue as well.

Whoa... Bro it doesn't work that way... You can't port away compression. Yes, a higher exhaust port will give a lower cranking pressure on a gauge, but the engine is still making the same big (dynamic) compression while running as it was before raising the ports.... meltdown time!

 

[shepster]

Hey, Chuck you still around ?
You have mail, ive got money to spend !

 

[SUPERTUNE]

I'll post back...This is the wrong week! to try and get ahold of anybody around here! Did you forget about DAYTONA and the Quote from racers (Freeriders Included)...If it wasn't for the last minute nothing would get done? Just swamped this week, just got home...Thanks

 

[shepster]

Ok sorry no worries, someone shoot me:banghead:

 

[yamaboy2000]

I never had luck with single carb engines in my race/freeride blasters, to much hull drag and load on the engine in left turns(common with sit-downs)..I would venture to say your squish really needs to be no less than .050 (.050-.060 ideally), compression sould not exceed 175psi(the difference between 165 and 185 is not even noticeable) and throw a set of totally stock/oem dual yamaha 38's on there and your problems will be over..hope this helps..