Montreal Manchild with an '81 Honda CB750K

If you are blasting it into the intake with motor running, it will get blown out of the exhaust. Seafoam does the same thing. If you are taking the plug out and filling the cylinder and letting it sit, you can then take the plugs out of all cylinders and turn the motor over to blast the cleaner out as well. Try it running, then the one bad one spray a bunch in the spark hole and leave it overnight, then in the morning leave the plug out, take the plugs out of the rest and spin the motor. put a rag over the one hole that had cleaner so it doesn't fly all over. Once it is all sprayed out, put plugs back and run the motor again till warm then test compression.
 
also if you do this and the rings are bad, the cleaner is going to get into the crankcase and thin out your oil a bit so you might want to check it and likely change it. that depends on how much you fill the cylinder, how bad the rings are or aren't etc.
 
Nice one bud, I'll do that and will let you know how I get on. I'm going to be spraying into the intake, but will leave some sitting in the cylinder overnight as well as a hail mary =)
 
Just finished a valve clearance check, replaced a few shims and now have 0.005" clearances across the board. Emptied a can of Honda's carb/combustion chamber cleaner into the carb intakes and compression check now looks better -

#1 - 140 (130 before)
#2 - 150 (same)
#3 - 165 (150 before)
#4 - 165 (150 before)

Question - although the compression has improved, cylinder #4 now has a cold exhaust, whilst the others are hot after running the bike for a while. Ok, not cold, but only mildly warm. Plugs on #3 and 4 look a little oiled.

Weird?
 
Dude I've been thinking that it could be the carbs. I gave the bike a once over when I bought it last month (new plugs, battery, bit of a spruce up on the carbs to clean out the gunk but nothing major, clean gas, airbox etc) but that's it. When I bought the bike it hadn't run for three years, and I just wanted to get it started.

Read in a different thread that someone was having a similar problem (theirs was a SOHC but the issue was the same), and that also boiled down to carbs. Is there a quick test I can do to see if the carbs are indeed the problem? How about cranking the engine, with only the plug from cylinder 4 removed, and if I can't smell any gas coming from the hole then that might point to no gas being fed from its carb?

I'm going to be doing a complete rebuild on the carbs next, but first wanted to make sure the valve clearances were as dialled in as possible.
 
The plug wont tell you much. Assuming these carbs have throttle plates you can bench sync them with a paperclip to get all the butterflies to close/open relatively the same. This will get you "close enough" but the best way to get them dialed in is with a manometer setup for a 4 cylinder bike.

https://www.amazon.com/Vacuum-Carburetor-Synchronizer-Gauge-Yamaha/dp/B004MSJ7E6

Here's an example of the process I'm referring to:

https://www.youtube.com/watch?v=t0qf11BOx6o
 
Bench synch and vacuum synch are firmly on the road map, first I'm going to rebuild the buggers as the gaskets and a few of the jets look rougher than a stucco bathtub

Thanks for the link - do you own one of those things? I'm thinking either I'll see if I can borrow one from my local shop or maybe build my own - there are a few vids showing how to rig one up with some glass bottles and a bit of know how. It doesn't show you psi or anything like that, only that the carbs are all pumping out the same pressure (shown by the liquid levelling out in the bottles)

By the way, yesterday I broke the mirrors off my Honda CB, 'cause I didn't like it looking like I looked twee
 
The Jimbonaut said:
Bench synch and vacuum synch are firmly on the road map, first I'm going to rebuild the buggers as the gaskets and a few of the jets look rougher than a stucco bathtub

Thanks for the link - do you own one of those things? I'm thinking either I'll see if I can borrow one from my local shop or maybe build my own - there are a few vids showing how to rig one up with some glass bottles and a bit of know how. It doesn't show you psi or anything like that, only that the carbs are all pumping out the same pressure (shown by the liquid levelling out in the bottles)

By the way, yesterday I broke the mirrors off my Honda CB, 'cause I didn't like it looking like I looked twee

I believe the homemade device you are referring to is for a 'wet test' that shows the actual fuel level in the carbs (for float height setting), not an actual vacuum pressure reading. You should be able to reuse all the jets, even if the surface is somewhat tarnished they will polish back up and you are much better off using factory brass than anything you'll find in a rebuild kit.

I bought one of those gauges when I was working on the GS550 i had a while back, never used it because the starter on the GS makes it an absolute pain to get to the sync ports, so I just sold it running off a bench sync LOL. The manometer setup was sold to a member here for pretty fair price. You may be able to borrow one from a dealer if they even have one kicking around, depends on how friendly you are with 'em. I use a single gauge with a 2-way valve to sync the carbs I have now (since I no longer own an inline-4).
 
The gauge looked like this -

https://www.youtube.com/watch?v=GaTRyHxvneY

Kudos to the guy - totally Macguyver'd it. Looks like it'll do the job, but like he said it's a good idea to use glass bottles, and not to let the liquid double back into the engine. That would be baaad.

Still leaning toward borrowing one of the real deals =)

Got the carbs finally to seat in the head boots - now all pipes are hotter than Louisiana asphalt, just like they should be. So the cold pipe was def a carb situation - once my Randakk kits show up I'll work on rebuilding them (along with Mike Nixon's booklet on how to do it). Moving right along =)
 
Well, it was definitely the carbs. I followed some advice, opened up the vacuum cover on the offending carb, took out the slide, plastic ring, and small plastic bean-shaped cover and sprayed some carb cleaner into the 4 tiny jet ports - replaced everything and she fired right up, exhaust nice and hot.

I also realized that the rubber boots connecting the carbs to the head were really stiff, and made it very difficult to properly connect the carbs. So I heated them up with the wife's hairdryer (about 5 mis on each), and then gently prised them off using a large flat head screwdriver. Once off, I heated them up for about 45 mins in front of my 4800 watt shop heater, clamped them back onto the head, and the carbs popped right in there, no worries.

One small step for man...
 
Been tearing into Rhonda, stripping her down slowly and getting to the point where I want to mock up the rear end and decide on what length suspension to fit in. Here's how she looks now -



A previous owner chucked some 11¾" shocks on the back which is all fine and dandy but they ain't gonna cut it for the build I have in mind. I want to raise the rear to give the bike a straighter look, thinking 14" - 15", but trying to figure out which size to order.

Is there a trick to playing around with the rear end to mock up how it'll look with different length shocks? 2x4's between the tire and frame? Just want to play around with height adjustments before I order the suspension.

Thanks as always,

-J
 
a couple strips of 3/4' ply wood with holes drilled would give you an idea. you need to watch for chain bind/rub but I think stock your bike had 13" shocks so yo umay get to 14" and be ok
 
Cool, I'll do that Maritime, thanks again, - amateur hour question but what happens if I remove both rear shocks at the same time? Will the frame drop onto the rear wheel? Anything I should know/look out for? How would I install the plywood - just lift the rear end up until I can fit the plywood lengths into the shock bolts?

And how would I know what is the max shock size I can fit in?
 
You can use this stuff but be careful because raising the rear that much will screw up the handling, these bikes are very susceptible to altering the trail which raising the rear will do. I would keep it at the stock angle and modify the seat position to give you the look that youy want.

Brian
 

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The Jimbonaut said:
Cool, I'll do that Maritime, thanks again, - amateur hour question but what happens if I remove both rear shocks at the same time? Will the frame drop onto the rear wheel? Anything I should know/look out for? How would I install the plywood - just lift the rear end up until I can fit the plywood lengths into the shock bolts?

And how would I know what is the max shock size I can fit in?

With the bike on the center stand you should be ok taking the shocks off, if you don't have one, prop it up on some blocks of wood so the rear wheel is off the ground. Like Crabs said be careful not to go to far past stock ride height, just going back to the stock size shock will fix the look for you I bet.
 
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