Why does my carb slide stick?

[thrownchain]

Maybe a previous owner put it in a vice with pressure across the mounting flange, tightened the vice to hold it, not realizing the warping of the carb body?

[viclioce]

Ed. Looking at your pictures on my phone they are cut off, almost in half on the right side. I'll check from my laptop when I get home. Like I said earlier, there was a situation where the sticking would come and go. So I am not surprised it would take 5 seconds for the slide to drop. I also wonder about the difference in width side to side vs. fore and aft. Did you have difficulties with screwing the top on and or off?

So are there ways to "adjust the carb body for the shape having gone oval? And can you tell if it is just at the top or through the entire length of the slide tube?

Finally, is it repairable at all or do I need to acquire a new carb body?

Continue to ponder it all you like. No rush to send it back. If you have a similar 24mm carb you can send me to replace it I would consider it. Something I could pull the remaining parts from that one and use to build another. Also as soon as the snow ends, I can head to Colorado next week to pick up the Ace 100 and a possible Road Toad and I talked to the owner up there about a possible carb. He may have an extra Super Rat carb of the same design and if he does I will talk him out of it. Or maybe another 24mm carb. We'll see how that goes as well.

I would like at some point to change over to an original 28mm carb and intake manifold since it has a Model 95 cylinder and head on it. Then I can change out the piston and go full piston port configuration with this motor. ; D Victor

[viclioce]

Another thought comes to mind. The Model 95 cylinder has a Model 94 intake manifold on it to mount this Model 93 24mm carb on it (that's the way I acquired it). Could it be the differences in these parts caused the warping of the flange and when tightened down cause the warping of its shape? Just my brain turning because I don't have any way of accurately measuring the parts. I'm relying on your years of experience with Pabatco to guide my on this. If I'm wrong let me know. If I'm right, really let me know and I will change everything because I do t want to warp another carb! ; D Victor

[Bullfrog]

Thrownchain, on the basis of your post - I examined the carb (again ) for evidence of DPO (Dreaded Previous Owner) vise squeezing or dropping or hammering . . . and I'm just not finding anything of the "smoking gun" type of evidence. This carb seems to have come from a WPO (Wonderful Previous Owner) - strange for sure, but it appears to be true.

So, currently, my leading theory on the deformations which have been found relate to the possibility of the WPO having been named "Scotty". Perhaps a transporter mis-adjustment reconstituted the carb in a warped manner once upon a time. I just haven't found any evidence of excessive or inappropriate application of force! And no evidence of excessive heat either.

There IS one thingI've noticed which I'm examining/mulling/thought experimenting . . . photos will follow in the next few days . . .

Vic - I can't find any damage to cap or carb threads . . . and no, I haven't noticed any problem threading on the cap. At least not any more than normal. Mikuni carb caps ARE a bit fiddly to get started on right - especially when the starter circuit lever is in the way (and seat and pipe and wires and throttle cable are working hard to keep you from aligning the cap properly and turning it at the same time). It is too early to deliver a long term prognosis on the carb . . . more examining, measuring (like deep in the carb slide bore) and mulling is required.

NOTE: This is an interesting little puzzle! (and unusual!)

Ed

[viclioce]

OK. I saved the photos to my phone and could see the whole of both images. I'm beginning to give creedence to my suspicions in the second post above. So now I really need to know if the mix of parts could have caused the tweeking, warping, mis-shaping of the carb body. I certainly don't want this to continue to happen in the future. I suppose lapping would make the flanges mount easier in the future, but maybe I should just get a spiggot adapter and change everything to 28mm and go from there. Let me know what your thoughts on this are. Victor

[Bullfrog]

No, Vic - don't worry about the part "mis-match" concept. The 24mm carb was bolted to an intake manifold which was produced to accept that particular carb -- no mis-match there.

If the Super Rat intake manifold bolted on to the CW cylinder - meaning the 4 manifold studs lined up properly - then there was no mis-match there.

The situation I've noticed (and want to study further) does relate to the following factors: 1) age of the carb 2)number of install/remove cycles the carb has experienced over the past 4-5 decades 3) the amount of torque applied to the carb flange mount nuts 4) how many of the install/remove cycles involved flat washers between the nut and the carb flange 5) other? Some of these things can not be quantified (um, like 4 out of the 5 items! ) -- but they all have had an effect on the condition of the carb flange (and perhaps the body??? - more mulling needed).

Ennnnneywayeeeeee, mounting a chrome tank Super Rat intake manifold and carb on a Combat Wombat cylinder is not an inherently bad match . . . and would certainly NOT directly cause the situation with this carb all by itself.

Ed

[viclioce]

My understanding is it's a Model 94 Wombat intake. Yes it lines up with the bolt holes on the cylinder. However there was always some difficulty getting the mounting flange on the carb to slide cleanly past the threads of the bolts on the intake manifold. I am now guessing someone over torqued the carb repeatedly in the past and warping the flange caused the clearance issues on the carb with the intake bolts.
So if the problem continues with another carb I will certainly do some additional lapping on the carb flange to make sure it slides on and off past the intake manifold bolts easily.

So is this carb body salvageable or do I need to let it go to its resting place and buy/build another one? That's the only question I have left. I'm assuming that since the slide bore is out of round it's trash, and continued use will cause continued sticking of the slide. So I'll be looking for another carb and manifold.

I am still hopeful that I can get a carb from my new friend in Colorado. But I'll also keep watching eBay do another flange mount VM24xx. There is one there now but it's the body of the carb which looks VERY rough. So I'll keep looking. And yes, please send the carb home to me when your done! Chances are I will use a lot of the imternal parts, slide, jets floats, etc. in my processing of whatever carb I pick up. ; D Victor

[thrownchain]

I don't think you can put enough torque on the flange mounting to cause that much compression of the carb body, no matter how many times you unmount and remount the carb. Still think it was squeezed at some point, maybe in a "soft" faced vice of some type.

[Dale]

Or possibly, this carb was flawed in the manufacturing process and missed by the quality control person (why does Lucy comes to mind?)?

[Bullfrog]

Thrownchain, I understand your thoughts . . . and they seem at first flush to be the most reasonable and likely . . . but the evidence of a vise squeeze just isn't there. You will find it hard to believe the very visible effects of "cold flow"/deformation of the zinc(?) die cast metal in the flange in the immediate vicinity of the mounting stud slots. Photos will follow to illustrate the rather amazing plasticity/ductility of the metal.

Vic (or others), in the meantime - can you provide me with the "inside dimension" between the studs on a standard Model 94 intake manifold? (caliper measurement between the two studs - inside edge to inside edge). Thanks in advance.

Ed

[Dale]

43.25mm

[Bullfrog]

Ah-ha! Thank you Dale. Very illuminating information - and quite helpful to assist in analyzing the situation with this carb! More information and photos will follow in the next day or two (or three).

Ed

[viclioce]

Ed. Glad Dale jumped in with the measurement needed. The best I could have given you was a best guess based on measurement with a steel metric ruler. Not having basic calipers is proving to be an issue and I guess I will go out and purchase a set.

You asked how many times the carb was mounted with flat washers. I can not answer this at all because when I recieved the bike the carb was being held on with nuts & lock washers, not flat washers. Whether or not flat washers were used prior to my ownership I cannot attest. And when I tightened the carb onto the manifold I always stopped at the compression of the lock washer and no further assuming that was enough. I can not address the WPO's treatment of same, but the bike was in terrible condition, having not even been started in 5 years prior to my inspection before purchase. The WPO even tried to start the bike with fuel and oil in excess of 5 years in the tank. ; D Victor

[vmxken]

Most oval bore carbs didn't arrive on the scene until the '80s so clearly, as always, Hodaka was just way ahead of the curve, so to speak.

[junker2k]

Ed, Is the 'O" ring channel the same size all the way around? If carb had been vise squeeze I would think that should be deformed also.
Just thinking
Jack K

[kingdve]

Just for a bit of info not that it likely applies here but my B+ had a intermittent sticking throttle problem . If I kept it to half throttle or less it was fine but half or over it would stick and slowly come down . While puttering around the field trying to figure it out I had left the top cable boot up while rechecking the cables for hangups , found the old boot had shrunk and was grabbing the idle pin cotter pin if it rotated around just right ...

[viclioce]

Interesting but not applicable in my situation. The slide sticks even when the cable is disconnected and the top of the carb removed. Ed has already determined there has been a change in the shape of the slide tube, possibly caused by pinching or over torquing the carb mount flanges. The horizontal bore of the carb venturi is taller than it is wide and this transmitted to the inside of the slide tube also being oval instead of round. But thanks! ; D Victor

[viclioce]

OK. I have one last question for Ed before you pack the carb up and send it back. What is the diameter of the slide tube to the nearest .001 and what is the diameter of the slide itself to the nearest .001? I would like to know if there is insufficient space between the dimension of of the slide and the slide tube bore. I would suspect there needs to be at least a .001 to .002 clearance on either side of the slide as it passes through the tube to make sure it doesn't stick. Is this a fair assumption?

If the slide tube is say, 27.500 and the slide diameter is say, 27.490 then the difference would be .010. Dividing that in half would be .005 in space all the way around the slide when inside the tube. Someone said earlier that a .001 difference can make a difference in whether or not the slide moves freely. That seems to be a bit of an extreme statement to me, but I could see if there was a difference less than .005 all the way around the slide. Just curious. Let me know if I am on the right track with my thinking. ; D Victor

[thrownchain]

So Ed, what's your theory ?

[Bullfrog]

Dang! Other more pressing activities have pushed the mulling/theorizing to the side for the moment. But I got all the photos and measurements I think I'll need to document the issues. The carb is on it's way home now.

Vic - measurements from a Super Rat 98 NOS carb suggest that total clearance for the slide in it's bore ought to be 0.1mm (0.0039" - round that to 4/1,000ths or 0.004"). Your most recent message starts with an example with a diameter change of 0.01mm, which is only 4/10,000th of an inch (0.0004") - gotta watch those conversions and decimal points!

Your carb exhibits 0.002" to ZERO total clearance in the fore-and-aft direction between the slide and bore - with the tightness at the bottom. Total clearance in the side-to-side direction ranges from 0.0043" (pretty proper) to 0.0051"(a bit loose) - with the tightness at the top. I haven't looked up the coefficients of expansion of zinc and aluminum, but I think aluminum "grows" more than zinc for each degree of heating. If that is correct, then the slide will "get bigger" than the hole as the carb heats up - and if we start off with ZERO clearance at 65-70 degree room temp . . . it wouldn't take much engine warm up to complicate the problem.

"Cold flow" of the flange metal over the decades is nearly as large a problem (hmmmm, maybe a larger practical problem). The heavily warped flange can be corrected - but will lose a full mm of thickness when lapped flat - which will allow it to deform more easily in the future (not to mention the lost depth in the O-ring groove and the effects that might have). Soooooo . . . I do think you are heading the right direction to replace the carb body . . . and use this one as a wall decoration or some-such.

Ed
PS: Photos will follow. (Vic-dimension notes were packed with the carb)

[viclioce]

OK Ed. Thank you to your in depth analysis. Sorry I got out of control with my decimals! I was typing quickly with my thumbs on the iPhone!

The 2 carb's should arrive here at about the same time. Hopefully my slide will fit the replacement carb, or, the replacement has a 2.5 slide as well. I forgot to ask. It's coming set up for around 4,000-4,500 feet so I will at a minimum most likely have to change the main jet. I'll see what size pilot it has in it when it arrives and change that as well if it's not a 35. The old carb was running a 35 pilot and a 140 main.

The bike was running well when the carb didn't stick. But it's still geared too low with a 13 tooth countershaft sprocket and a 56 (??? need to recount it) tooth rear sprocket. So the bike was topping out at about 45-47 mph on the roadway. I believe Danny told me stock for a Model 03 was 15/52 if I remember correctly. So I'm going to order a 15 countershaft and see how she runs first, before thinking about a smaller rear sprocket. Right now, first gear is almost (not completely but almost) useless. Taking off in 1st gear only gives me about 1-1.5 seconds of use in first gear before reving out and needing to find 2nd gear!

I'm still not sure I understand how a warping of the intake tube can cause a warping of the slide tube, but your statement that the slide tube itself is out of round with minimal to zero clearance cold completes the story for me. The carb body shall indeed become a wall ornament!

Little by little, with all the help I've been given, I will get it dialed in. ; D Victor

[viclioce]

Actually, I don't think I ever specified mm or inches when expressing my decimals! I reread the post again and did not! ; D Victor

[hodakamax]

Victor, zero clearance is the same in metric and standard.

I couldn't resist.

Maxie

[dcooke007]

Max,

Go to your room and no more posting until you learn better.

Danny

[viclioce]

Now Danny! Don't pick on Max! At least he got something right! LMAO!!! ; D Victor