Topic: CB750A Street ET bracket drag bike. A year to build it.

[Bill/BentON Racing]

Well I'm  ,just scanned,wrote notes went to post all gone!~~!!!!
Here we go again,gimme 10 minutes,I need a shot!,Bill

[Jim F]

Here we go guys
put in your ear plugs and hold on

Not sure why there are two videos
click on the second one

[Bill/BentON Racing]

If @ first you don't succeed....here we go:

Well let me tell you about it
Run 1,the way it came off the track,12.94@ 116.14. 74.10 RWHP Rich and midrange way rich and up and down
Run 2,changed air jet orifice size to # 50. 74.99 RWHP,So rich in midrange off the chart,and still screwy looking.
Run 3,we change the mains from 127.5's to 122.5's.
Checked needle position,dyna 6 clip needles,were in #6 position,moved clip up to # 3.
Fuel screws went to 2 from 3.
As you see,it seemed to like the changes,Main jet real close,bottom end much better,midrange still fat,but at least above the line.Made 2.65 RWHP more than base.
Brian commented twice on strong motor and WHO built it?
He agrees 10+ more hp there.
Drum roll for Frank,his first comment.......weaker springs!! and sync carbs spot on.
87=RWHP next Saturday!!! Jon,Mike,Sam,too busy too call,but want your input!
Still wouldn't pull above @2,500 RPM's w/brake on,but felt crisper and harder to hold back!
We made progress,Thanks to all,esp Brian and Sheila,real good people and of course Big-Jim,Bill

[Doctor_D]

Nice work folks.  87rwhp... maybe... but right now you're where I was with my smaller cam and it's not a bad start.

And, yes, tuning spring rates in CV carbs makes all the difference in the world.

[scottly]

Frank,2600-2800 rpm's.

So the higher stall speed was with curve #1, correct?

No Scott, I think it was on #5, best to ask Billy.

Sam.

[Bill/BentON Racing]

Frank,2600-2800 rpm's.

So the higher stall speed was with curve #1, correct?

No Scott, I think it was on #5, best to ask Billy.

Sam.

Scottly,I believe Sam's right.# 5 seemed to pull 2600,need to check to be sure.Bill

[scottly]

If a timing curve change resulted in a stall speed change of 200-300 RPM, I would be very interested to know just which curve was used in both cases.
I see this ignition also has a switch activated retard feature; an old car drag-racing trick was to wire a switch to one set of points in a dual-point distributor, which would retard the timing at the end of the strip, increasing top end speeds. Sounds wrong, but it works, and there is science behind it: by the end of the quarter, the combustion chambers are very hot, the load from wind drag is at it's greatest, so the fuel burns much faster. Faster burn=less timing advance.

[jweeks]

Bill,
     Good progress in the midrange. I'd be dropping the needles down as needed after testing with the softer springs. Rpm vs horsepower chart available? That would be more helpful than mph. What are you planning for softer springs - cut down or swap to? Would really like to see horsepower in the 7k to 10k range to help determine how much we can overrev the powerband on the top end.(gearing) Did you play with the total timing at all? I don't think that there's another 10 horses on the top end, but there is more to be found in the midrange. That will make a more significant change to ET than where it peaks at. Let's get the syncing done!
     Thought that I might have gone a little too far on the air idle jets. Still #52 to #50 was fairly close. Didn't know that the needles were on #6. This is why I'm so very happy for the dyno time!    Still think that we're just not making enough torque in the 2,600 to 3,500 rpm range. Make your changes and retest if you can afford it. Once we have all that we're going to get, you can try a test and tune somewhere local. See how the 60' times repeat. If we're still generating random numbers, we will need a powerband shift down.
     Sam - just what was done today, I'd guess about a 2 tenth quarter mile improvement. With the gearing change, I'm thinking 4-5 tenth improvement. Sync, softer springs, dropped needles, total timing check, and there may be another 2-3 tenths there. We're getting down to where I thought you'd be. It was in the pictures on the dial-in board.   

                                                                                           JW

[jweeks]

Clarification: 2 tenths for the tune, 2-3 tenths more reduction with the gearing change, and maybe another 2-3 left in the tune. 6-8 tenths better than the 12.94

                                                            JW

[dragracer]

JW,
Do think the bike has high 11 second potential???

[Bill/BentON Racing]

Jon,thanks,we're on the right track!
Don't forget the "white leathers" another .2
12.94- 1.00 = 11.94!!!!!!!!!!!!!!!!!!
Damn,does it sound good @ 10,000 rpm!!!!
We're booked again next Saturday.
We will be in the 11's by Valdosta!!!!!!!....November Cup
Thanks for all your help.Bill
I'm sticking with my 11.98!!!

[jweeks]

Bill and Dragracer,
     I've stated it before - No I don't think that it will run 11's. I would like to be proven wrong. Give me a density altitude about 500' below sea level with a tail wind, maybe then?  Adjustable cam sprocket may get us there. The biggest challenge is that the minor change in the idle circuit fuel/air ratio hasn't significantly changed the torque at around 2,500 rpm!  That's why we can't launch any harder. A couple of more teeth on the rear and dropping the needles a couple of notches will really help beyond where we currently are with the midrange. To get 11's requires several tenths reduction in the 60' times. Where is the power coming from to do this?  More compression, more stroke, and/or less cam? None of the options are cheap! Getting the midrange closer will help some with the 60' times. I just don't think that we'll find enough bottom end to get there. We may find another mph or two on the top end when we're done. It will get more challenging to launch as we find more bottom end. If we find enough to get into the 11's, you won't be able to hold it on the starting line with the current brake setup. 12.1's best in good air. That's my opinion.

                                                                                             JW

[Leino]

Who's the pretty lady in the pictures?!? 

[Bill/BentON Racing]

Jon,Mike thanks,on fuel,that's where we planned to get 4-5hp....you right on the money.
Jon,you forgot the "white leathers".12.1- .2 = 11.9!!!!
Wish I was staging rather than typing!
Carb sync today!!
Jon,that last run two weeks ago I believe no look back,no chop would have lowered ET .2?
12.7 I think,we take off .8 from 12.7 = 11.9....that # again!!
Jon,going full lean on needles and play w/timing,add right fuel w/proper additives,2 teeth more rear,massage carb slides and bores,add 2 more return springs,sync spot on, I want a pic of that smile when we break into the 11's @ Valdosta..... ,Bill
Sam....wake your sorry azz up!!
Oh and weaker springs! Z beautiful lady is Brian's wife!

[Tintop]

Thanks for the post Bill, great info.  Sounds like you had a successful 1st dyno run, and got lots of good info for more improvements.

+1 on MikeR's comment regarding gas.  Are you using pump gas from the local station?  I would assume that Street ET requires 'pump gas', have you tried using 94 race fuel with no ethanol?

Ok we have Bill @ 11:98, and JW @ 12:01, sounds like a pool.  I'm in at 12 flat, 121.2 based on that English guy's reaction times.

[Bill/BentON Racing]

English guy? Oh Rip Van Green,I think he'll wake up soon,needs his rest ;)I shouldn't talk,this time 2 weeks ago I was asleep @ the line....  .5 someting reaction,I went when Jon hit me w the cattle prod! I did remember to twist the throttle tho once he prodded me! I can't wait to need mo brake!!!! ,  Bill
Jon,someone post dyno run on youtube!! Thanks,all the world should be privy to that sohc hymn!!

[dragracer]

Jon,Mike thanks,on fuel,that's where we planned to get 4-5hp....you right on the money.
Jon,you forgot the "white leathers".12.1- .2 = 11.9!!!!
Wish I was staging rather than typing!
Carb sync today!!
Jon,that last run two weeks ago I believe no look back,no chop would have lowered ET .2?
12.7 I think,we take off .8 from 12.7 = 11.9....that # again!!
Jon,going full lean on needles and play w/timing,add right fuel w/proper additives,2 teeth more rear,massage carb slides and bores,add 2 more return springs,sync spot on, I want a pic of that smile when we break into the 11's @ Valdosta..... ,Bill
Sam....wake your sorry azz up!!
Oh and weaker springs! Z beautiful lady is Brian's wife!

Leave the carb jetting alone for now, add the weaker springs but go with oxygenated fuel. You will see the results you've been looking for:

Personally i would try the MRX01. Lots of my sportbike friends use it with great results. The only caution is the fuel must be drained from the tank and carbs at the end of the race day and replaced with regular fuel or it will clog and gum up anything it comes in contact with. The other viable and cheaper option is to use the U4.4 which doesn't have to be removed from the fuel system. U4.4 is what i intend to use in my ZX10 when i get it put back together.
http://www.vpracingfuels.com/motocross-racing-fuel.html

[jweeks]

Bill,
     What gas are you looking to get another 4-5 horses from? Oxygenated race gas? Overlapping posts here. Just left my track's rules meeting today. VP c10 gas this season $9.75/gallon.(110 octane) And that's the cheap stuff....?

     No, street ET doesn't require pump gas. I'd rather see Sam's happy face at Valdosta.(11's) If you see mine there, probably I'll be racing something...

                                                                                        JW

[jweeks]

Another clarification - VP110 not C10 @ $9.75 locally.
     Bill, remember that the dyno operator won't like sniffing leaded gas. Sensors die quickly with the leaded race gas.  No, I don't believe that the chop was worth 2 tenths.  On a clutch bike - yes, on an automatic - no. You only lose a little over .015 per mph you wipe off. At least I do on my Hondamatic...
     Dragracer - any fuel recommendations?

                                                                                    JW

[jweeks]

I'm typing faster than I'm reading. Thanks Dragracer for the recommendations!

                                                                                             JW

[754]

Nice numbers outa that motor.!

 Warning..thiswillmakeYousick...

 A week ago a working dyno same make as that sold here in town for 900.00 +25%.. had the late model air/fuel thing with it..



 Bad part was the dyno computer was in a batch of 14 computers, the lady had to buy them all at 140 +25%.. to get the dyno computer..

 So she is in for 3800ish.. with 13 computers left to sell.. hey she might get it for nearly free...

 

[Jerry Rxman Griffin aka MuthaF'er]

Don't you guys have the Megacycle 125-75 cam in it? Isn't that more of a top end cam? How would the 125-65 respond in it for your mid-range?

[dragracer]

I'm typing faster than I'm reading. Thanks Dragracer for the recommendations!

                                                                                             JW

Jon.
You know how drag racing goes, everyone has their own thoughts about what does and doesn't work. I know the oxygenated fuels work great and give extra horsepower throughout the rpm range. The one drawback is some of this fuel is expensive and will be an ongoing expense whereby making internal modifications is a one time deal but could be more costly upfront. Since it is a race only bike, i would go with the MRX01 for the best results overall. But never, never leave it in the tank or carbs after a race. Remove it at the track before you leave for the house and run some pump gas through it for a few minutes and its good to go. Most guys have the battery operated siphon pumps they use to run it suck it out of the tank and back into the 5 gallon pail. Just be sure the gas tank is clean or you'll contaminate the clean fuel in the drum.

The bike is already a bit rich so the MRX01 should be perfect wirthout a jetting change as they recommend richening when using this fuel.

[dragracer]

Guys, i got a call from Keith this afternoon. He was distraught. It seems between the time he left for sork this morning and around noon, some azzhole thief came along and stole his trailer with his bike and tool box. This wiped him out as far as race stuff.  I think there were some pictures of his bike posted on this site by Jim or Sam. Please take a look back through this thread to familiarize yoursleves with the way the bike looks. Its a CR500 Honda 2 stroke- very unique.

Contact Voodooracer through this site if you ever see this bike.

All i can say is i can't stand a damn thief!!!!!!!!!!!

The bike has been recovered as of this morning- great news for Voodoo.

[Bill/BentON Racing]

Jerry,yes 125/75.125/65 might work better on automatic.
Dragracer as usual on the money,those are the 2 fuels we'll be looking at.
I just saw Keith's bike recovered! ,gotta read post still.
OK,Jon,we'll try to prove you wrong!!!
Sam,you awake yet?
Off to sync carbs.Bill