exhaust getting soft on my 80 MNS

[Brian]

Tried to isolate this weirdness and thought I had it a couple times, but now it is happening non-stop. Symptoms- First off, Cylinder 2 is running significantly cooler than the other 3 (although #1 is a bit cooler than 3 and 4). I have an infrared thermometer. Secondly, the exhaust is flowing stronger out of the right pipe than the left pipe. 3rd- barely runs with choke off and can't accelerate throttle even in neutral.

Pulled carbs and thoroughly cleaned - removed and soaked MJ, PJ, Richness screws, sprayed Berrymans in all ports, also ran cleaner in fuel (it's still in there). Tried to look and clean from all 4 directions or each carb. Set all richness screws to 2 3/4.

Things I checked. Also noticed the pick up wires were original (you may remember this bike sat in a leaking shed for 20 years and only had 2010 mile on it) and so I replaced with thicker DVM wiring top 2 and bottom 2. Moved wires 1 and 2 to 4 and 3 respectively and problem stayed with 2. Checked compression 2 weeks ago cold and all around 160 to 175. Checked again warm today and they are 162 to 180.

Let's back up. I ran this last summer and it now has 3,500 miles on it. Ran real smooth but didn't have the power of the 2 78's I had owned in the past.

I also cleaned most or all connectors but have not replaced the fuse panel. Since this problem stays with #2 with wires switched, must be carb, or maybe valve- but compression is great. Also switched slide and diaphragm with #4- no change.

Signed- head scratcher.

[jetmechmarty]

I wouldn't hurt to check the valve lash, but the problem is your carburetor.

[Schming]

Hi Brian, the symptoms you described tell me that the pilot jet circut still may need cleaning. Also the starter jet in the float bowl is a cause of the "won't run without the choke symptom.

Have you set the floats fuel levels ?

[motoman]

I wouldn't hurt to check the valve lash, but the problem is your carburetor.

Yeppers.............float bowl ACTUAL fuel levels are all whacked and not the same and to low. would be a good start. Your idle mixture settings were my first clue,(being opened way to far)in order to get fuel. Then it comes all at once with to low fuel levels in the bowls. Idle mixtures SHOULD tune in correctly approx. 1 3/8 to a max of 1 1/2 turns out from seated with those later model carbs. Those idle mixtures NEED to be set individually at operating temperature and at an idle!

[Brian]

Thanks everyone! I realized after I posted that I should have told you about the floats- They ran all last year set at 21 so I measured each individual float and they are still at 21. If anything that should be rich, right? I could bend the tab down to make them all 23 if everyone agrees.

For the richness, I wrote down 2 3/4 in my book as what the original setting was and probably got that wrong (maybe after trying to get it to run less lean). I will reset each- thanks! The consensus seems to be that white plugs are cool but given a choice, I am more of a mocha guy.

While I'm at it, any other clogging areas I should check?

Much appreciated,

Brian

[crazy steve]

....I ran this last summer and it now has 3,500 miles on it. Ran real smooth but didn't have the power of the 2 78's I had owned in the past....

No, and it won't. The '80-up bikes were significantly detuned compared to the '78E. The '78s had the most power, they were detuned every year after that due to increasingly stiffer emission requirements.

[Brian]

thanks Steve, and I meant to write that I had 2 79's in the past, but I totally agree. the 80 seems a bit subdued. I am hoping when I get the tuning right, the difference will be smaller.

I do have one last question I have been kicking around- what if I switched over to the longer needles and 115 mains? thinking the WOT would be a bit better. Was planning to wait till I got everything right with the original MNS set up, then decide.

Here's to an early spring,
Brian

[MaximPhil]

No, and it won't. The '80-up bikes were significantly detuned compared to the '78E. The '78s had the most power, they were detuned every year after that due to increasingly stiffer emission requirements.

Hi Steve,
My 81H ,as the last of the breed, may be slower but it sure hauls my fat arse around in a hurry The Dynojet kit installed by my guru made it not just run but stay in tune which it refused to do before.
Phil

[TopCatGr58]

Hey Brian,

Aside from the #2 carb being suspect, a few other things to check.

George(GloweVa) holed a piston a year ago because he hadn't realized that the bolts securing his intake boots had come loose and had gotten some extreme leaning affect! Those bolts can come loose. Also, are the boots in good condition? Next, the vac. port caps on the boot can dry rot/harden and leak as well....can still be stuck on the brass nipple, but actually be loose on it allowing vac. leak!

You said you swapped wires...which ones..the plug wires I would assume, but just wanted to be clear since you talked about the PU coil wires as well, but like you said the problem stayed with the #2 cylinder. You also mention a little reduction in temp on #1 as well. That also points to possibly a fuel delivery problem...fuel lines, petcocks, inlet "T" between the carbs, the screens under the float valves clogged, etc.! Yes, 21mm's does sound too low/too rich, yet you adjusted your pilot screw out fairly far beyond stock range. The pilot jets and circuits are easily clogged/gummed.

T.C.

[Brian]

Thanks Topcat and Everyone! I was out most of yesterday and have been trying to further dissect the issue(s) this morning. First, Here are answers to great questions:

1. Several great suggestions (Topcat, etc...) on possible intake leaks. Bolds are tight but intakes are weather checked and have not thoroughly tested the vacuum plugs, BUT - more info. all the plugs are black- worst on #1, least on #4 which is also now the coolest. #2 is fine on temp now. Exhaust is soft on left side. I replaced all new plugs last weekend, and today I switched 1234 with now 4321. problem still on left side (soft pooping on my cupped hand behind exhaust).

2. Electrical - I swapped 1 and 2 with 4 and 3 respectively. also cleaned some contacts but the fuse box (and fuses) are somewhat corroded and I should replace all. WHAT ABOUT THIS- what if I have a bad solder joint on on 1 of my pick up wires, and it happens to be the wire that provides the spark to #1 or #2. and when I switch the wires, the #1 (or #2) still takes the spark from the same pick up coil, based on timing. BTW, I checked the timing and it is perfectly on "F" at 1100 rpms.

3. Remember it only runs with choke on! so black (or not tan) plugs could be a result of having to run the engine with full chock initially (I always run it up until 2,500 RPM's) then go to half choke. I can slowly give it gas with full choke on an rev to 4k (would probably go higher) but cant crack the throttle. When on half choke, can't rev - starts to die. With no choke will try to run at 400 rpm's but die and cant idle higher or rev. So, on second thought, I guess this could be a lean condition- maybe... and the plugs are black from having choke on. sure acts lean when I try to rev it, but that could be a rich bog. And, if it's rich, maybe I need to pull all 4 carbs and bend the float plate to lower the floats to 23mm??

4. I should not use the fact that is ran decent all last year as a reference because- this bike was all black in the carbs after 20 years of sitting with gas/ lacquer in it. And I did not pull the pilot/ richness jets till carbs were back on the bike (I know rooky mistake). I drilled the plugs, sprayed the holes with cleaner and started tuning at idle. But I bet you they were still clogged all year until I pulled the carbs and deep cleaned 2 weeks ago.

BYW, I now don't feel as frustrated or alone in this major challenge, so THANK YOU!!! I know this challenge, frustration and cost is greatly reduced with your help and support! (although I will probably feel like a dork when we find the problem)

Brian

[TopCatGr58]

Hey again Brian,

Okay, the pickup coils control 1 ignition coil which controls 2 plugs at a time, and they both fire at the same time, so it's very rare to have 1 plug go out on a paired set. And since you swapped the 1-4 and 2-3 wires to opposite plugs, and the problem stayed with the cylinder, that sorta rules out the ignition.

Next, take a look at these photos of the 80 carbs cut apart, you can see how small and intricate the passages are, and why they need thorough cleaning to ensure fuel/air will flow thru them. Being unable to get throttle response is a sure indicator that the passages are NOT clear or clean. Did you actually take apart the carbs including the emulsion tube...the large brass tube that the MAIN JET screws into, it's called the Main Jet NOZZLE?




These are of 79 carbs, but show the jets and parts in place:



Also, when you took apart the carbs...were there any rubber caps on the PILOT JET towers next to the Main Jet? There were some bastardized carbs during the production transition from 79 to 80 that still had the sharing tunnel between the main and pilot jet towers, and requires the rubber tower plugs. But once they got thru those bodies, the true 80-81 carbs do NOT have the sharing tunnel, and the pilot jets feed directly from the float bowl and not thru the main jet, and so the rubber caps are NOT required.

Next, aside from cleaning the carbs...did you replace any parts, or use any carb kits? The K&L kits are notorious for having the wrong sizes, they don't match the genuine Mikuni sizing, and run too large for the same listed size which runs them too rich for pilot jets. Speaking of Jets, what sizes are you running?? The 80 should have the 42.5 pilot and 110 main stock.

Also, are you running the OEM airbox, or aftermarket POD filters? The Cheap Emgo brand have a prominent lip on the mounting side that interferes with the carb inlet ports!

T.C.

[Brian]

once again, thanks Topcat for taking the time to share your expertise!! I will focus on carbs. The reason I was wondering about the Pick up coils is that since we have 4 wires (and I admittedly don't know exactly how they work), I thought there maybe 4 separate PU coils. Then, even though I switched 1 and 4 for example the single PU coil that sends the signal to the coil at the right time for cylinder 1, could still be weak and #4 wouldn't care because it only uses the 2nd spark from the #4 PU coil. so if it's 2 pick up coils vs. 4, then I agree with you.

For the carbs, I sprayed the crap out of everything but did not remove the emulsion tubes. Also my carbs do not have the plugs for the pilot stem and do have 42.5 pilots and 110 mains. I will pull them sometime tomorrow hopefully and do another thorough cleaning and adjust the floats by bending the middle little tabs.

Thanks again! /Brian

[Brian]

GREAT NEWS! I believe I found the problem. While tapping out the emulsion tubes (with a screw threaded in them) the number 1 carb had something fall out- it was half of the emulsion tube!!! evidently is was sitting in there broken for who knows how long and hidden from view.

How does a completely stock bike that sat for 20 years break and emulsion tube? Not sure but glad I had the help of this site to find it.

Does it make sense that that's the problem?

Brian

[Brian]

BTW, they were black and really needed cleaning! My bad for not doing that sooner. Paid $29 for 1 delivered on ebay, but it could have been worse. I'll clean up the other 3.

[Radioguylogs]

Cause for Black Emulsion Tubes

Backfiring for some reason? Broken emulsion tube caused by backfire?