1989 VMAX carb fouling and rebuild.

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jeffwat

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I did this write up so that if I ever need to do again, it’ll be available.
My 1989 VMAX wouldn’t run anywhere near idle without choke starter. After several partial clean attempts, I gave up, totally removed carburetors, and rebuilt. This is a summary of parts of the rebuild that I hope make it easier for others. My bike is now running absolutely great.

1. From the start, before you do anything, and then while taking apart, take many pictures, so
You put it back the way you took it apart. I took about 60 pictures, camera right by bench.
a. For instance, when I got the front two carburetors separated from the rear two,
I took pictures of the linkage, with red markers, tape, on connect points so there was no
Confusion on re-assembly.
b. I backed off the synchro screws as much as possible, counting half turns, so I could re-
assemble in the same condition. Don’t remove screws all the way, or you have 3 more
springs to deal with (backing screws). Sync will still be off when you re-assemble, but
you’ll be a lot closer, and you’ll re-synchronize at the end. Cover with your hands or a use
rag when separating carbs, so the synchronizing springs (3 total) won’t fly everywhere. I
baling wire attached each spring to it’s respective carb so I wouldn’t lose them. Don’t lose
circlips on link ends connecting carbs 1&2 from 3&4. I put them back on after removing
the link.
3 4 return springs bottom view gen details.jpg
1 2 synchro springs.jpg

c. There’s also a fourth spring on the return throttle cable.
Return spring throttle cable 2437.jpg


2. After carburetors are removed from engine, be sure to stuff a rag in each manifold hole, don’t
want anything falling into manifold. Also, clean up area around V Boost, while you’re at it.

Some Special Tools:
3. I had a few tools I consider especially useful, see picture below:
a. I bent one of throttle outside cables bearing down on undoing screws with Phillips (I was
able to straighten out). Note wooden blocks; I thereafter set carbs on these blocks, and on
re-assembly so as to have them straight and even, and not break/bend anything.
b. My oxyacetylene tip cleaners, other jet cleaners were too small for the pilot jet (about
0.008-0.0095” ID). My stainless welder wire brush has 0.008” strands. I snipped off a
couple, used the wires, held in surgical tools to clean out the pilot jet in each carb, plus all
the main body small openings.
c, The `T’ rubber fuel hose: I was concerned about tearing after all these years, so instead of
`pulling’ ends off, I used a thin blade to get them started, then used the reverse pliers to
easily `push’ the tubes off. The reverse pliers were handy in many places.
d. Screwdriver with big handle, tight fit on Phillips did the trick, but note the socket with a
Phillips on the end. That’s the tool for being able to bear down, and precisely, slowly
break Phillips screws loose without stripping. [ I loosely put ALL screws back in their
original holes, so as not to lose any of them]. Get a friend or wife to hold carbs steady,
bear down, and use the socket wrench to undo screws slowly. They will pop loose. Undo
all screws to loosen, but then gently re-tighten. When all screws have been broken free is
when to finally start taking them out.
4. My idle jet screws already had the brass plugs removed. You can read elsewhere in the forum
on how to remove plugs. I didn’t want to close the screws to measure them (to not compress
any sludge), so I used these calipers to measure from Carb body down to top of idle screw.
For instance, my No. 2 carb idle screw head was at a depth of 0.951” with the slot at 11:30.
That way I could just back idle screw out, but put it back exactly the same on re-assembly.
DSCN2453-tool-1-for-web.jpg

Now for some more tools.
5. I got the surgical clamps at a hot rod show, very handy, If you look closely, you’ll see a wire strand in each one – one is straight, the other is bent at 90 degrees. That’s how I cleaned all the very small orifices. They were also very handy for placing the synchronizer screw springs on re-assembly.
6. Anti-seize: I don’t care, not going through heavy wrenching again. I dabbed with toothpick a small amount of the stuff on all threads on re-assembly. I access screws on the assembled bike, to check on occasion. Not going to strip any threads. I did not, however, use the anti-seize on brass air pilots, pilot jets, idle screws (just oiled idle screw), or main jets.
7. The pick with red handle easily removed little O rings, got to places my fingers couldn’t.
8. The wire has a small bend at the tip, and was used to remove the small steel washer and rubber O ring that didn’t come out with the idle screw on a couple of the carbs.
9. I bought an idle screw set, and a pilot jet, mostly to see what they looked like. For the bigger screwdriver I bench grinded it to EXACTLY FIT the idle screws, and also all the air pilots, main jet, and main air tube. The small screw driver I ground to EXACTLY fit the pilot jet inside the float bowl. I was able to safely remove all; it took a bit of grunt, but they all popped loose. A tight fit was the key.
10. After you loosen the jets, stick a tooth pick into the hole to unscrew it the rest of the way, and also use the toothpick to get them back in.
DSCN2454-tool-2-for-web.jpg

THE REBUILD:

I have my service manual; you can download a manual. I basically followed the manual.

I got a plastic box, with many small, removable internal boxes/lid, to place each parts section in its own box (idle screws, enrichment circuit, float parts, etc.). Do what you want, but I did one carb at a time, checked and rechecked. Take your time. If you make a mistake, you have to take it all apart again.

I’m not going in to explain everything in detail, the manual does, but:
1. When you take off the left side panel behind the false air scoop, be gentle, those electrical parts are expensive. I wrapped blue paint edge tape around the whole panel, and taped it aside.
Left panel control modules.jpg

2. Behind the above black panel, the little black plastic box has a transparent white cover you have to remove to disconnect the cables going down to the carburetors. The screws are itty bitty, really in there. Get solid backing, tight fit screwdriver, and remove gently. The screws are pretty tight. There are two cables, and mine are marked incorrectly! So, mark one side with tape from the throttle, and from the carburetor, so you put them back the same way. I accidently switched mine on re-assembly, and throttle worked backwards.

3. Loosen the boot clamp on each carb bottom, on the carb side only (not manifold end) all the way. The clamp backing nut won’t fall out (Assume you’ve already removed air box side.). The carbs can be hard to pop up and out. Get a big fat bladed screwdriver, and there are flanges on each carb that you can pry between the flange and rubber boot tops, while pulling up on each carb a little at a time, and they’ll pop loose. At this point, I’ve only disconnected main fuel line from pump. Disconnect the others later. With the cables disconnected, you can lift the cable outside tubes out of the slots by the carbs, lay them down on the side, and you have a lot more room to remove the carbs from the left side. Go gentle; watch out for hanging up on electric cables on right side.

4. I took carbs apart, but not the main body throttle bodies, and also left throttle linkages attached. Also I took out the choke starter plungers, but did not take off the plunger bodies. Your choice, I just didn’t feel the need, as the choke starters were the only thing that were working smoothly.

5. Starter Choke Linkage: The shafts and links for the choke plungers, a few issues: Carb No. 2 (Front left) has the friction screw that holds choke position. Before unscrewing it, note carefully the sequence of washers, Teflon/nylon (?) and steel, take a picture, or you’ll be rubbing your head wondering on reassembly. Also, there’s a tension spring for the shaft for carbs 3 & 4; note little washer locations. The levers for the starter plungers are held by small Phillips screws on the shafts (shafts have indents). Mine were REAL tight. Don’t strip heads; grab with strong tweezer nose pliers to unscrew if necessary. Shafts are flimsy, support them. IMPORTANT: Each carb has a small flanged Teflon bushing to support the shaft, and they’ll fall out usually as you remove shafts. There’s also a flat Teflon washer (they could be nylon). Anyhow, do work on a clean table, watch for them, remove them. I taped all these parts with blue tape to the starter shaft assembly, and just set it aside.

6. After removing enrichment systems, float cover, float/needle, jet body, all jet body parts, CV diaphragm, air jets – each in a compartment, I sprayed the carb body with a carb cleaner (acetone/toluene) (outdoors, rubber gloves, protective glasses) inside and out. Then I used the surgical grips with small wires to clear each orifice. Amongst the four carbs, I found couple of the orifices just below where the CV diaphragm was plugged (Purge jet no. 2). I then shot this carb cleaner through every orifice. They’re inside the float chamber, top throat of carb, a very small one in enrichment part of body,
Float Chamber 2450.jpg Enrichment area 2451.jpg

and inside CV chamber. I ran the wires through and through, sprayed with cleaner, then ran bottled gas in a can through each (I don’t have a compressor). Also, note that in addition to the hole in the carb throat where the idle screw is, if you manually move the spring loaded throttle plate out of the way, you’ll find 3 very small holes in a triangle pattern. I ran the wires through all of these, carb cleaner, wire, air, until they were clear. I was quite satisfied, and in fact do not believe there was much of any plugging except as noted above in the entire carb body set. This was not my problem area.

All of the metal other parts I put in a carburetor chemical parts dip solution for an hour, including float cover. Parts came out like new. My rebuild kits had new float needles, but I kept in reserve, as mine looked fine. I replaced almost all of the gaskets.

It turns out that my problem was that all four pilot jets were plugged. I unplugged them with the wire strands, back and forth repeatedly, then chem. dipped them, then squirted carb cleaner and bottled gas until each jet had a solid stream.

Left picture: Idle jet assembled: spring, steel washer, and rubber gasket, pre-cleaning. Right picture: Jet Block mounted inside float chamber. The
pilot jet, second brass from left was totally plugged in all four carburetors.

DSCN2446 idle jet only.jpg DSCF2122-jet-block-for-web.jpg


The little black plugs in jet block housing (above, right photo) I did not replace. They looked OK, fit fine, and when remounted, they can’t come out, as the carb body blocks them.

Note the two marks on the jet block body above. The lower mark is very close to where the liquid level is supposed to be, and the upper mark is where the pilot jet orifice ends up. So, the orifice is in a vapor space after shutdown. If left for long, the gasoline evaporates, air will intrude, and foul/oxidize those little holes. A problem with four carbs for one engine is VERY small idle circuits (~0.008” -0.0095”), and there’s NO WAY to clean them except to take it all apart. Best ideas I’ve heard for our bad ethanol type gasoline is to at least turn on the ignition every few days to activate the pump and fill the carbs, displacing any air with hydrocarbon fumes. Nevertheless, each time you do that, the heavier ends of the gasoline remain, and the float chamber will have a heavier gasoline inside. Take a small amount of gasoline – open to air, set it outside, and look at the dark brown liquid you’re left with after a day or so. A bit of an exaggeration, but instructive. So, at least every couple weeks, you need to fire up the bike. For longer periods, drain the carbs, siphon the tank (put it into your car). I use stabilizer, but I don’t want to have to do this job again for many years, if ever.

SOME RE-ASSEMBLY THOUGHTS:
General: The previous job – not mine – had inadvertently mixed a couple pilot air jets. Be sure you put them in right. Also, my main jets were slightly different than the manual, but the bike ran fine for me at speed, so I left them alone. Your call. If you have V Boost issues, must fix now.
1. When putting back brass parts, be firm, but don’t go crazy.
2. When re-assembling jet block, be sure screws are good and firm, all parts in place. Mount the float and needle.
3. Information in the forum shows where the assembled float, holding upside down, has a distance of 1.117” from the outside (farthest from needle side) float top to the carb float chamber top flange. Three of mine were perfect, the fourth needed about 3/16” adjustment.
Float level.jpg


4. When putting float in, with needle installed, be sure float engages the little wire clip on the float needle, or you’ll be taking it all apart again.
5. The float rests free, so you have to hold the carb body lower, and lower float chamber cover onto body. You can damage the float if float comes off part way when you’re putting on float cover. The float cover contorted O ring is fussy to replace. There are small indents to hold it, in the cover, but I also put axle grease in the grooves (just a bit) to help stick it in place. Go careful; be sure it stays in place on assembly. I had to do one a couple times before I got it right.

Float-cover.jpg


6. The float cover has a brass plug that can be removed for main jet replacement. Remove this plug, replace O ring, but be sure aluminum face against O ring of cover is smooth, or it may leak. I had to dress up one of mine due to corrosion. Then tighten down firmly. Again, if you err and it leaks, you’re going to be taking the whole thing apart again.
7. For re-assembling the carbs together, it’s the reverse of course, but what helped me:
a. Blue paint tape to hold synchro springs in place helped, plus the surgical clamps.
b. When assembling carbs, and before you mount assembly brackets, I put the `T’ fuel line
on to the carbs. Otherwise, you really have to contort the rubber T to get it on, and I
didn’t want to do that.
8. Every screw hole had a small dip of anti-seize, and all screws were mounted loosely.
9. Be sure to assemble the throttle cables to carb linkage on carb 2 before putting front and back carbs together, or you’ll have a hard time.
10. With the carbs loosely attached, and synchro screws backed out, I put in the 3 synchro springs, the ones I kept attached with baling wire. When I got one in place, then I immediately screwed in the attendant synchro screw to hold it in place. The surgical clamps really helped me. I also installed at this time the small return throttle cable spring.
11. I did most of this assembly on the two wooden blocks, turning carb set upside down or upright, as needed.
12. When it was all assembled loosely – including the choke starter shafts and levers – I made sure my wood blocks were on a flat surface, then slowly tightened down all the screws.
13. At this point, I used idle adjustment screw to open master carb (no. 2) a bit, and put a feeler gage between each throttle plate, made minor adjustments to synchro screws so they were somewhat the same – about 0.003-0.004” open.
14. Either put some oil, or some silicone spray on the inside of the carb boots, and a bit on the carb bases, and you should be able to install carbs without too much trouble, bearing down on each carb a little at a time with one of the wooden blocks, and they’ll pop in place.
15. With clean idle screw passages, I first put screws back in to the proper depth I’d measured before takedown. Then I closed them, and found the left side carbs 1-3/4 open, and the right sides set at 2-1/4 and 2-5/8. I decided to reset them all at 2-5/8 open, as I always felt they were too lean.


STARTUP: leave off air box for first startup.
1. I have a fuel pump tester, and checked, and my pump did 2 quarts/minute (jeffwat: Wrong, pints/minute, not quarts a minute), and dead headed at 5 psi. Fine.
2. Because of my severe fouling, I siphoned tank, put gas into truck (ran fine). I checked bike tank bottom, looked fine, and started with fresh gas. My fuel filter was chocolate brown, and I replaced it.
3. I used ignition several times to cycle fuel pump, fill fuel bowls. If one or more of the floats hangs up, you’ll know it, because it’ll keep on pumping. Sorry if that happens to you. Mine closed right up.
4. I watched for about 15 minutes with a small mirror, looking for leaks – no problem.
5. I then started bike, it was a mess, running all over the place, and I was confused. After about 15 minutes, I was able to get it to run at about 1500 + RPM, quit and shut it down. No leaks.
6. I installed air box and all attachments, and proceeded with the synchronization with a Motion Pro Synchro Pro system.
7. I followed the video carefully, read instructions, and the procedure worked great. I found my carbs were BADLY out of sync, and I had to very roughly get carbs 1&2 balanced, couldn’t even see vacuum in 3&4, so adjusted between left and right side, then balanced 3&4, then got idle down to 1100, then did a couple more times around. The point is, best I tried, my carbs were WAY off initially, but it took only about 10 minutes of adjusting, and my engine runs dead smooth at 1100 rpm, starts easily, idles great. I WIN! HAVE 100 MILES ON BIKE, AND IT’S LIKE A NEW BIKE.
ADDENDUM: Because carb set will wiggle around a little before it sets in, I'll re-synchronize in a couple months.
ADDENDUM 2: I put a few extra pictures related to rebuild in my album, so you can see additional views.
 
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Following this writeup I think I could even come out on the other end with a working bike. Great work!
 
Thank you folks for your comments. I haven't done a public write-up before, and appreciate the feedback.

Guys who do these rebuilds often or work in the trade have experienced most of the things I mentioned. But, doing it the first time on some of these older bikes can be daunting, not the least of which is concern that the parts are EXPENSIVE, and some parts you might break will be very hard to find.

I also feel having the right tools are very important: forcing out a pilot jet with a sloppy fitting screwdriver and breaking the pilot jet instead means an `Easy out' (they're not !) and a lot more work. Been there, done that.

The items I discussed are those that can become very frustrating if overlooked, or done hastily or wrong and something breaks.

Thanks again, Jeff (jeffwat)
 

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