Bridgestone Motorcycle Parts Discussion Board
Bridgestone Tech Talk => 175 & 200 Talk => Topic started by: skiri251 on July 26, 2016, 04:11:16 PM
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After 250 miles of break-in as per the owner's manual, I put the new spark plugs in and tried to go a bit quicker (~ 55 MPH on level ground).
After 3 miles of running, the plugs looked completely white.
So I changed the MainJets from 95 to 100 and also raized the needles 1 notch from the middle.
After 5 more miles, they look like as in the pics.
Right cylinder looks good (tan) but what about the left (white and black insulator).
During all this, I smelled something burnt. It's not typical 2T oil smell but smelled rather worrying.
I measured the head fin temp with IR thermometer and left side was 120C (250F), right side was 110C (230F).
Is this normal or too hot?
As for the engine power, I felt a bit disappointed. This is 200cc 2T but on per or a little more power than my '68 Honda CL125A (4T twin).
Certainly I felt much less power than my 1978 Yamaha IT175 (2T, single).
Meanwhile the gas mileage is around 35MPG.
I checked the compression and both sides were around 140PSI.
Is this what I expect from BS or something is seriously wrong with mine?
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It should have a great deal more power than either of the bikes you mentioned.
Something must be wrong.
Are you sure it is running on both cylinders?
Randy
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Must be running on both cylinders considering both exhaust headers are around 80C (176F).
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Hopefully nothing seriously wrong, engine compression seems good. Unable to comment on the engine temperatures but if it smelled really hot , it probably was. Also check nothing on the electrics is getting hot.
Could be any of a number of things. There is a good trouble shooting section in the Clymer manual for the 200, available on this site under Downloads. Also some good Service letters on poor performance, use the 175 versions. . Check everything over, don't assume obvious items like coils etc are OK. Should have far more performance than you describe. Be careful (which I think you have been) changing carb jets and settings, maybe try one change at a time and see what happens but make sure everything else is set correctly first I.E Timing, plug type, float levels, etc.
Good luck, Brian.
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Thanks.
The troubleshoot doc mentions worn rotary disk as one of overheating causes.
How worn is worn?
I don't remember seeing thickness limit value.
Are these considered as worn?
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There is a thickness spec for the 350 rotary valve (3.95 - 4.00 mm) in the back of the 350 service manual. I expect there is an analogous spec for the 200 and probably found in a similar location in the 175/200 manual.
...bert
Actually, I just looked for the spec for the 175/200, and I could not find one. Perhaps one of our 175 experts can weigh in here...
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Seeing the picture of the disc valve reminded me of this post. http://bridgestonemotorcycleparts.com/index.php?topic=3596.msg19395;topicseen#msg19395 (http://bridgestonemotorcycleparts.com/index.php?topic=3596.msg19395;topicseen#msg19395)
The discs probably are correctly timed on their drive collars but you may want to check. See the response from our late departed friend 'Disc Valve' for a quick method. On the face of it, the condition of your disc valve(s) looks OK, nice sharp edges and no obvious scoring.
You don't tell us what you have done so far. Have you checked the obvious things like air cleaner, mufflers clogged, points and condensers OK, ignition timing (can't say what it should be on a 200, anyone?), chokes shutting correctly, good fuel supply to carbs. Will the engine rev freely when ridden or does it bog down at speed. How much smoke from the pipes ?
Brian
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The bike came to me as a basket case.
Crank rebuilt by Scott Clough with new bearings, rods and an oil seal.
Left cylinder replated by Millennium.
Right cylinder looked okay so I just re-used.
New pistons, pins, rings, and bearings.
New bearings and seals in the tranny.
NOS ignition coil pack.
NOS points.
NOS cam.
New condensors.
Rebuilt AC generator with new bearings and seals.
Podtronics 3 phase R&R.
Used UNI foam with K&N oil for air cleaner.
New petcock.
NOS float valves, main/pilot jets, needles, idle air screws.
Timing set as per the notch in the crank disk. (I don't have the factory tool so just used a piece of metal. May have a degree or so error because of this?)
Point gap 0.016" as per Clymer.
The disks are correctly installed as the photos show (I took them during assembly.)
Currently it runs like 125cc 4 stroke (okay but not powerful.)
I installed Chinese electronic tach and according to that, the engine struggles to rev above 7~8K RPM.
Low RPM torque is poor. (even on slight uphill, I need to slip the clutch to move from dead stop.)
Both exhaust headers are blued.
Smokes around the same from both exhausts.
I checked defusers and exhaust pipes. Scraped carbon as much as possible. It was just a thin layer on the wall anyway.
I don't describe it as "clogged".
Ran without the defusers for an experiment but no change in power (other than the bike sounded like Suzuki GT380.. LOL)
One thing:
I had leaky float bowls so I used a carb I got from eBay.
The cylinder on that carb side didn't fire unless I choke it with my fingers. Once it started firing, it was okay and I could ride.
So I gave up on eBay carbs and back to the ones came with the bike.
I ended up installing two gaskets per carb to stop gas leak.
I don't really have confidence in the current carbs I use. Maybe they are really tired?
I cleaned then with cheap ultrosonic cleaner from Harbor Freight.
I also put thin wire through carb orifices to clean.
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Update:
I installed brand-new VM18-144 carbs.
Wow what a difference!
Just came back from nearby twisty. 5th gear, 50MPH and climbed the hill with ease.
I think the nasty smell is gone also although head temp remained around 120C (250F).
And the gas mileage improved dramatically now it's 61MPG! (it was constantly 35MPG with old carbs.)
So whatever it was, tired old stock VM17-18 carbs weren't performing. Worn slide/sleeve? I didn't feel anything unusual though.
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That's more like it, she should be good for nearly 80mph. on a good road. Glad you've sorted it.
I you feel she is still running hot, check for over advanced ignition timing with a dial or depth gauge in the plug hole. Can't tell you what the measurement should be.
The starting problem with the Ebay carb is likely to be a blocked jet at the bottom of the cast tube in the float bowl. Clear the slant drilling in the bottom of the main float bowl first, if that doesn't do the trick use a piece of thin piano wire to clear the jet down the tube. There are drillings in the main body of the carb that can't be reached with a wire, possibly one of these was blocked on the old carbs. I don't know if ultrasonic cleaning will clear these. I have a pair of water damaged carbs that may give me the same problem in due course, time will tell
Enjoy your 200, you've put a lot of work (and no doubt money ;D) into her, good luck, Brian.
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Always glad to hear of a successful sorting! Congrats and enjoy the ride!
Just for curiosity's sake, where did you find the new Mikunis?
...bert
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Thanks every one.
I wish I could keep stock carbs.. I can try cleaning old ones but at this stage I would rather ride. A little tired of detaching/attaching carbs.
You can find VM18-144 on eBay. If you do the search, a few sellers show up.
Sudco has them too. (probably a little more expensive..)
This is a current Mikuni product they still manufacture, not old stocks left in warehouses.
The ones I bought came with #70 main jets. And apparently it is the right size for 200RS too.
I tried #105 and #95 in the beginning, and they were way too rich.
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I you feel she is still running hot, check for over advanced ignition timing with a dial or depth gauge in the plug hole. Can't tell you what the measurement should be.
I tried it. Factory shop manual has the numbers (for 175 but I guess 200 has the same stroke..)
According to that, mine is a little retarded.
But I am not sure I setup the dial gauge properly. It is so sensitve near TDC.
So I relied on the notch. (I don't think Scott Clough assembled the crank disks misaligned.)
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OK sorry to dredge up a 6 month old post.
But I just got a new set of carbs.
They also came with 70 main jets.
Which seems awfully small for a 200,
The stock carbs were running 95 jets
I was going to stick 100's in but reading this I'm now not
Sure.
Are you still running 70's or have you changed them?
Also did you stick with the stock 17.5 pilot jets, or keep the new carbs 30's?
Cheers
Logan
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I thought the Pilot Jet was supposed to be a #20 (VM22/210-20)? Also, the manual calls for a Main Jet of 90(4/042-90) or 95 (4/042-95).Can anyone tell me if the following is correct for the VM17-18 carbs: Needle Jet for the 175 = O-0 and Needle Jet for the 200 =O-6; Throttle Valve = 2.0 (VM18/158-2.0) where 2.0 indicates a Cut Away of 2mm; Float Valve (or Needle Valve assy) =1.5 (VM15/172-1.5);?? Also, would the correct P/N for the Air Adjusting Screw be VM20/305 and the Jet Needle be #4F18.?? I've ordered new bowl gaskets that are supposed to be for a VM18 carb but neither fits the VM17-18 carbs. Both gaskets a little different. I have purchased several used VM17-18 carbs off of ebay. One was off of a Kawasaki 175 Bushwacker and had ordered a "Keyster" carb repair kit for it. HOWEVER, the bowl gasket does NOT fit. I found a NOS VM17-18 carb on ebay but it's not set up for the 175/200. Thanks...........Tim
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OK sorry to dredge up a 6 month old post.
But I just got a new set of carbs.
They also came with 70 main jets.
Which seems awfully small for a 200,
The stock carbs were running 95 jets
I was going to stick 100's in but reading this I'm now not
Sure.
Are you still running 70's or have you changed them?
Also did you stick with the stock 17.5 pilot jets, or keep the new carbs 30's?
Cheers
Logan
Yes. I am still running #70 main jet. Pilot jet is #30 which came with the new carbs.
I tried #105 and #95 main jets in the very beginning but they were way too rich. (The engine hardly rev'ed above idle.)
The only thing I changed is the needle poistion. It's at the top notch (lowest needle position.) Otherwise there was a mid-range hesitation.
I am located at near sea level.
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I thought the Pilot Jet was supposed to be a #20 (VM22/210-20)? Also, the manual calls for a Main Jet of 90(4/042-90) or 95 (4/042-95).Can anyone tell me if the following is correct for the VM17-18 carbs: Needle Jet for the 175 = O-0 and Needle Jet for the 200 =O-6; Throttle Valve = 2.0 (VM18/158-2.0) where 2.0 indicates a Cut Away of 2mm; Float Valve (or Needle Valve assy) =1.5 (VM15/172-1.5);?? Also, would the correct P/N for the Air Adjusting Screw be VM20/305 and the Jet Needle be #4F18.?? I've ordered new bowl gaskets that are supposed to be for a VM18 carb but neither fits the VM17-18 carbs. Both gaskets a little different. I have purchased several used VM17-18 carbs off of ebay. One was off of a Kawasaki 175 Bushwacker and had ordered a "Keyster" carb repair kit for it. HOWEVER, the bowl gasket does NOT fit. I found a NOS VM17-18 carb on ebay but it's not set up for the 175/200. Thanks...........Tim
Please note that we are talking about new VM18-144 carbs in the latter half of this thread.
As for old VM17-18:
> Needle Jet for the 175 = O-0 and Needle Jet for the 200 =O-6;
Yes, I think so.
> Throttle Valve = 2.0 (VM18/158-2.0) where 2.0 indicates a Cut Away of 2mm;
The ones I got (with the bike) came with throttle valve cut-away of 2.5
> Jet Needle be #4F18.??
Again, the ones I got came with 4J4.
I am not sure what I got here is the stock however.
Maybe the experts will chime in.
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Here're the VM18-144 setups came with the carbs as I bought:
Genuine Real Mikuni 18mm Round Slide Clamp On Carburetor Carb VM18-144
Standard Jetting Specifications
Carburetor # Venturi Size Main jet (VM4/042) Pilot Jet (VM22/210) Needle Jet Jet Needle Throttle Valve Air Jet Needle Valve
VM18-144 18 70 30 O-0 4F18 1.0 2.5 1.5
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well,
i put a 100 in and the original 17.5 pilot and the orignal needle,
ran like a bag of nails, started first kick, but wouldnt even take off.
ill change the main and pilot jets to 70 and 30, but keep the old needle,
and let you know.
never would have thought that a 70 was even close to big enough.
but she's stupidly rich with a 100 in there.
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never would have thought that a 70 was even close to big enough.
but she's stupidly rich with a 100 in there.
That was my thought too. LOL
But even #95 was way too rich.
Must be the venturi design change?
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Got to ask ---- Did Mikuni use a revised numbering system on the later carbs for mains, pilots, needles etc.
Also found these on the UK Mikuni site - UFO inserts. Not available for 26mm carbs (yet?) but look pretty simple. Just smooths out the bottom of the carb slide and cuts turbulence with significant performance benefits ????? Might interest Rod (Husker) and others including me ;).
http://www.motocarb.com/ufo-insert.html (http://www.motocarb.com/ufo-insert.html) Brian.
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UFO inserts. Not available for 26mm carbs (yet?) but look pretty simple. Just smooths out the bottom of the carb slide and cuts turbulence with significant performance benefits ????? Might interest Rod (Husker) and others including me ;).
Don't do it! They completely screw up the whole jetting system. It can be fixed with different main jet, idle jet, needle jet, and needle. Just count on many hours of trial and error to get the job done.
It's really not quite that bad, but it will take a few new parts and quite a bit of time to get it right.
My brother put those in his CB350 just before Daytona one year, bad mistake.
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Thanks Karl, the message is clear. Did your brother ever sort the CB ?
Even so, as a gas flow engineer, I can see the logic. Could effectively simulate the fitting of a bigger carb !! with increased air and fuel flow, at very little expense and no engine modification. Maybe when I've got a spare GTR running and time to play, I'll give it a try. Our buried carbs won't help. Brian
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He did get it mostly sorted after another race weekend or so and they may have helped a bit. He never had dyno data. He had a very aggressive camshaft that caused some valve spring problems which didn't help matters any. Trying to jet the bike with broken valve springs didn't work well. He did have the fastest CB350 in AHRMA for a while.
The UFO inserts do sound like a good idea. The smoother flow across the needle and jet seemed to change the jetting characteristics significantly, and not proportionally across the full range, so everything had to change. The idle and low to mid opening curves apparently change quite a bit. Trying to get idle, low throttle and roll-on correct was the biggest problem. They've been around long enough that there may be more data on what specific changes should be used to start with. He was trying them in 2002/2003?, not long after they came out.
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2003? Didn't come across them until now, maybe not quite the 'magic bullet' they had hoped for. Bit like the Wal Phillips fuel injector from the 60's but worth further consideration. Brian.
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Speaking of fuel injection, I think someone that has a decent understanding of the electronics involved could adapt a couple of the units from modern dirt bikes to an old 60's/70's bike. The dirt bike ones don't need much power, some even work just from kickstarter speed generating enough electrical power for initial startup, so they don't need a battery.