Author Topic: Racer Resurrection  (Read 69554 times)

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Offline al_pritchard

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Re: Racer Resurrection
« Reply #240 on: May 10, 2019, 09:13:22 AM »
The needles are 4J6, and the clip is in the 2nd position (second from the top)

Going to re-set up the carbs and if the weather holds give it a go later today.
Al Pritchard
Highlands, NJ

BS175 Racer

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Re: Racer Resurrection
« Reply #241 on: May 12, 2019, 01:18:05 PM »
I tried a 4J6 needle out at Willow last month.

200 main
35 pilot
4J6 with the clip in the top groove

Too rich off throttle (3/4 to WO) and bike would bog

went to a 190 main and 30 pilot with no real difference

went to a 4J15 needle which is leaner with clip in the bottom groove and a 25 pilot with the screw turned in to about a 1/4 turn out

I was running a 4DH7 needle prior which is leaner still with clip in the bottom groove.

I use to run 4D20 needles which are really fat (lean) but the clips for those are bigger diameter for the relief in the slides I use and the needle would be raised a bit.

paul

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Re: Racer Resurrection
« Reply #242 on: May 20, 2019, 07:23:09 AM »
Hi Paul,

Could you take a pic of the various needles you have.

In the attached pic, the one on the left is a 4J5, the one on the right has no markings. It came as part of a VM22 repair kit I bought for a Kawasaki A1.

I am using VM-22's off a Kawasaki A1 250.

Thanks .. ray

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Re: Racer Resurrection
« Reply #243 on: May 21, 2019, 10:25:32 AM »
Hi Paul, Al,

After digging through parts here I found a few other needles to compare. It seems the needles in the Kawasaki A1 250 carb kits are close too the 4J6's.

Note the main needle jet - the centre hole that needle jet slides in is smaller than the 2.5 mm diameter of the needles ??...

ray


Offline al_pritchard

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Re: Racer Resurrection
« Reply #244 on: May 21, 2019, 10:49:06 AM »
Hi Ray

I was wondering what needle came with my rebuild kit. Guess it's a 4J6.

Was not particularly happy with the quality of the kit, overall. Some of the jets still had burs from machining in them. Decided to only use the gasket and put the rest of the shelf.

In the image below (click image for larger view) is the needle from the Kawasaki A1 kit I got. Next to a 4DH7, 4F15, and a 4J11. That 4J11 looks so short - no wonder it's so much richer than the others.


Al Pritchard
Highlands, NJ

BS175 Racer

Offline vinny g

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Re: Racer Resurrection
« Reply #245 on: May 21, 2019, 04:53:44 PM »
Hi Al. From memory I ran 4D3/4 needles in N size jet holders/needle jet. You can normally fine tune on the clip but certainly you won't need much richer (thinner) I'd look for around a 4D3 in a N4 holder. Incredibly important to get this there or thereabouts as you can change main jet all you want...it won't make a difference unless you're close with needle/jet combo. When I ran 22mm's I used slot head jets.. 110-130. These are diametric.. (100 is 1mm) With 28mm's I run 200-210-220 hex head. These are flow rated.

Quite a while since I ran 22mm's but I've probably got it written down somewhere and will dig it out. Certainly though...N size needle jet.

Cheers, Vince

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Re: Racer Resurrection
« Reply #246 on: May 22, 2019, 02:04:48 AM »
Hi Al .... all,

It's a pity the kits are not made a bit better and marked. Even a note in the bag would help ? We reproduced these to blah, blah, spec ...

Yes, found burrs & swarf. The air screw & spring measured up ok ??.... and the gasket.

A can of worms has been opened up on what needle jet to use ?

ray

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Re: Racer Resurrection
« Reply #247 on: May 24, 2019, 11:25:29 AM »
I'll try and get some pics of the needles I have in the next day or two.


paul

Offline BRT-GTR

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Re: Racer Resurrection
« Reply #248 on: May 25, 2019, 08:08:18 AM »
          Here's another tuning guide I found useful when setting up the GTO.  Again aimed at the Kawa triples but they use similar Mikuni carbs to our Bridgestones. Lots of stuff you will already know but has some good basic info on which way to go with jet/needle sizes . Also warns against the use of non Mikuni overhaul kits as Al/Ray point out.
             https://www.3cyl.com/mraxl/manuals/carbtune/carbtune.htm

          See the section on ''Effect of jetting variables'' near top and the tables right at the bottom which show dimensions of various series 4 needles and needle jet sizes. Might help to identify those unmarked needles although would require measuring to a 1000th of a mm!!
        Hope this helps, a can of worms indeed.                                               Brian.
« Last Edit: May 25, 2019, 09:16:29 AM by BRT-GTR »
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Offline SR-175

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Re: Racer Resurrection
« Reply #249 on: May 26, 2019, 03:18:48 AM »
Hi Brian,

Very helpful lead !!.... thanks ... ray

Offline al_pritchard

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Re: Racer Resurrection
« Reply #250 on: June 04, 2019, 09:15:32 AM »

And it's alive. No, it's not Déjà vu. If you are on the Bridgestone Facebook group you may have already seen this. But I thought I should upload it, and record the carb settings, and next steps.

Set Up
Pilot Jet: 20
Main Jet: 230
Air Screw: 1/2 turns out
Float: 25mm
Fule: 112 octane / VP C12
Oil: 28:1 / Castor 927

Did't do any carb tuning yet. Just wanted to get the first heat cycle in. A couple of notes, and things to do. She doesn't idle yet - not unexpected. I didn't take any time to start to work that out. She also stumbles pretty hard as you open the throttle.

I suspect as I start to get the idle set, it will help the 1/8 open throttle stumble. If I understand the tuning it's a combination of the height of the throttle valve and the needle jet.

And thats for that link Brian. It's helping me better understand how the carb works, and how to go about tuning it in.

Click image to view video
Al Pritchard
Highlands, NJ

BS175 Racer

Offline BRT-GTR

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Re: Racer Resurrection
« Reply #251 on: June 04, 2019, 02:41:22 PM »
            Congratulations on getting her running.   Here's how I went about getting the carbs right.
         Start at the bottom (idle) and work up the range to top end (main jet) with tuning. At 1/8 throttle she is on the top end of the pilot circuit.
             Suggest winding the idle screws up to raise the slides to a point where she will idle. Then adjust the airscrews, to give highest idle speed. Do one pot at a time, removing plug from other pot but ground the plug of the disabled pot on the cylinder head to avoid coil damage. Bear in mind this is a race tuned engine, it may not idle like a swiss swatch !!
   
           Ideally Mikuni say airscrew should be between 1-2 turns open. Less than 1 turn - pilot jet too small, more than 2 turns - pilot jet too big.  After adjustments you need to back off the idle screws equal amounts to give required idle speed.
             If a cylinder doesn't respond to the airscrew, the screw may have been overtightened at some time expanding its seat in the carb body (quite common in my experience). Not much you can do about this. With a relatively high idle speed the adjustment may be outside the range of the pilot circuits in which case set the best, reliable idle you can achieve.
              Once you are happy with the idle, move up the range . I wouldn't worry too much about the slide cutout at this stage, the factory went for a rich setting (small cutout), it may be OK. Come back to it if you can't get rid of the stumble. 
             Needle clip position/needle size/needle jet are the next items to play with, good luck.
« Last Edit: June 19, 2019, 07:38:20 AM by BRT-GTR »
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Offline SR-175

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Re: Racer Resurrection
« Reply #252 on: June 17, 2019, 10:33:45 AM »
Hi Al,

You can also toss the air screw into the bin. After closer inspection and trying to use it I have found the originals to be better. The tip diameter is not the same by about 0.15 mm.

Offline al_pritchard

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Re: Racer Resurrection
« Reply #253 on: July 08, 2019, 03:57:02 PM »
Yea, I didn't use air screw ether. Total crap!


Spent a little more time with her over the long holiday weekend. The goal was to get her idling, and take a quick run around he block

Got her running, and idling well enough - more on this below. And a good heat cycle in the engine.

But I couldn't get her to go anywhere. The minute you started to let out the clutch, she died. No matter how hi you held the RPMs, the moment you put a load onto engine she bogged out and died.

Back up on the bench. A quick pressure test told the story. 45lb of compression! Thats all she can muster from each cylinder. Pulling the heads you can see the oil drops outside the o-ring. So at least that explains why she can't move under her own power.

I think I cut the o-ring grove to deep, or to wide for the o-ring. So I'm going to take a little more off the head, and see if I can get her to give me something a lot better on a compression test.

The leak down test didn't show a problem. I guess because the leak down was about 4 or 5 lb. and the o-rings are holding at least 45lb.

Would be interested in what others are seeing from a pressure test.





Al Pritchard
Highlands, NJ

BS175 Racer

 


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