'85 Suzuki DT65 carb issue after cleaning. Is ultrasonic cleaning an answer?

[bassboy1]

I've been struggling with this issue for the past month or so. I've never run this engine - it came as a parts engine with another one I've purchased, but was told that it did run before.

I swapped this DT '65 powerhead into service on my outboard jet. I knew it had a carb issue, and a broken head bolt, so I took care of the head bolt, replaced head gasket, rebuilt all three carbs, and installed the powerhead. I did the usual stuff, replaced the fuel lines, pulled the known good fuel pump from my other powerhead, etc. Oil injection was already disabled on this powerhead (and pieces were missing), so I simply pulled the gear powering the oil pump, so it wouldn't be turning a dry pump. Carb jets and float bowls were soaked in a can of Gunk dip cleaner, and the main body had the spray can and compressed air routine.

After assembling everything, I couldn't get it to run. Compression was good, spark was good. Even replaced spark plugs, to be safe. No fire. After many cranks, plugs still came out dry, so clearly, no fuel. Finally got it to run on premix sprayed in the intake (this was on the hose, no load). There was clearly fuel in the float bowl, but it wasn't getting drawn into the intake. Finally, got it to run on it's own fuel by giving it a shot of premix sprayed in the intake, and it stayed running. After playing with it enough that it would consistently start, I figured a lake test with some Seafoam was in order. Thought maybe the reed valves were sticking, and it just needed to loosen up.

On the lake, couldn't get it to start at low revs. If I started it at 2/3 throttle and just took off (it's a jet, no issue to start in forward), it would run fine, and stay running until I dropped to half throttle or so. Ran perfectly throughout the top of the rev range, but wouldn't start in the bottom of the rev range, and would die if I tried to drop the throttle. I ran nearly 3 gallons of gas (with 6 oz of Seafoam mixed in) through it on that trip, and still no change.

Back at the shop, it will run on the hose, and stay running, but as soon as I put it in the test tank, it dies. I've gotten it to run as long as 10 seconds or so at idle under load, but as soon as I try to open the throttle, it dies. If I finesse the choke while trying to rev it up, I actually can get it to rev up under load, so it's clearly starving for fuel at lower rev ranges. I've played with the adjustment screws on the carb every way until Sunday, no change.

After the initial rebuilding, I've pulled them off twice since, to verify everything is correct, and to reclean them. I confirmed that compressed air is making it through all the ports I'm blowing through. Maybe a slight improvement after the reclean, but still won't run well enough to run. It will start nearly every single time, just dies in 2 - 10 seconds unless I really play with choke.

I have checked vacuum in the intake runners, and gotten what looks to be acceptable readings (my manual doesn't list anything on that subject). The fact that it runs perfectly at the top end tells me the rest of the engine is working well - it really has to be in the low speed side of the carb.

I've cleaned these things twice. Is there something goofy about these carbs that I'm missing, or is it a case of not clean enough? Would ultrasonic cleaning be a better alternative? Am I ignoring something simple?

 

[mphelle8vld]

You've reposted so members are missing some old information. Since you're chasing the same issue the previous owner had, I don't think the carbs are the problem. I would look at the TPS adjustment and then check that the timing is advancing as per the service manual. Like I mentioned in an earlier post, the 85-6 had issues with the labyrinth seals.

 

[bassboy1]

You were right on the money with the TPS. After reading your post, I decided to check it first. I did the continuity test, as defined in the Clymer manual, but what I noticed is that the wires have been resoldered (poorly) onto the switch backwards. My brown wire is on the inboard terminal (manual calls that #1) and the green wire on #2, but the manual is suggesting the green to be on #1 and the brown is supposed to be on #2.

Swapping the connections (plugging brown into green on both) seemed to have worked that problem out, for the most part. When I ran it in my test tank, it would idle great, and respond to cracking the throttle.

I just took it to the lake, and it idled great, started to rev up great, but would die abruptly once you got the throttle a few degrees open. Cut the throttle, and it would go back to idling great. After playing with it, I noticed that it died at the point that the #1 switch roller opened the circuit (rolled off the step). I then held the switch down while trying to rev it, and it revved fine. At that point, I simply unplugged the brown wire altogether, and the engine performed flawlessly. Idled well enough, responded to throttle all the way through the rev range, etc.

Not really sure what that means.

 

[mphelle8vld]

Good to hear some progress, I'm using the newer wiper switch so I can't remember the order of the two switches. The one that actuates first (as the throttle opens) is the idle switch, light green wire, should read shorted to the black wire with the throttle closed and immediately open as you turn the shaft. The other is the throttle switch, brown wire, reads open to the black wire until the shaft turns 12 degrees then it shorts to tell the cdi to advance the timing.

 

[bassboy1]

According to these pics, it appears that the #1 switch should be the timing advance after 12 degrees, and the #2 switch is the idle switch.

This also implies that the green wire should be on terminal #1 (timing advance) and the brown wire is the #2 (idle switch).

Mine were simply soldered in the reverse from that, which gave me the no run condition. Once I swapped them to match the above, it worked fine, up until the timing advance hit. My switch works properly, per continuity test outlined in the pics, as long as you use wire placement, not color, to test.


Correct me if I'm wrong, but it appears that by me unplugging the timing advance switch, I was just running on the base timing, not allowing it to advance. I don't understand why it would die the second it gives the command to advance timing. It sure ran well for the timing to not be advancing.


The only scenario that I can come up with is that the poor solder job was somehow grounding to the mounting bracket. I will repair all the solder joints on that unit before taking it out next, and see what that improves. It'll probably be early part of next week before I have time to take it to the water again, but I will report back.

 

[mphelle8vld]

The Suzuki service manual has a drawing the opposite of yours showing the acceleration switch on the inside near the metal plate. Regardless, look at the cams, when you first rotate the throttle whichever cam operates its switch first is the idle cam and it's switch should have the light green wire. The other cam will have to rotate 12 degrees to operate the acceleration switch with the brown wire. Black wire is common to both switches.

The motor will advance the timing with rpm, with the acceleration switch engaged at 12 degrees it will advance quicker.

 

[bassboy1]

Interesting. The idle cam is on the outside, and acceleration switch on the inside, so that would mean that my wires were correct originally.

Oddly enough, with the wires correct, it doesn't run.

With them reversed (brown connected to idle switch, green to timing advance), it runs well until 12 degrees of throttle.

With them reversed, and then the timing advanced switch unplugged (or plugged in with switch held down), it runs perfectly fine.

I did trace them all the way back the junction box, in case they were switched there, but the colors are correct all the way into the CDI unit.

I'll fix all the solder joints, and then retry them in correct position, reversed position and then one unplugged, and whenever I find the position that works best, I'll leave well enough alone.

 

[mphelle8vld]

Here's a photo of my original before I replaced it with the new version, it works fine if you can't get yours to work.

 

[bassboy1]

My switch is testing correctly per the continuity test you outlined, so I don't think a replacement switch is necessary. I neatly soldered the wires on (green on idle circuit, brown on timing advance). It will run fine with green connected to green, and brown unplugged. If I plug brown in, it acts up.

At this point, I'm just going to leave brown unplugged. We ran about 15 miles Friday night, with no issues, so I'm okay leaving it as is.

 

[99yam40]

you need to know what the timing is doing and if it is in spec

 

[bassboy1]

I get to chase down another new issue with this engine. I've been running this thing for over a year as we last left it (throttle position switch unplugged - it simply won't idle with it plugged in).

To follow up with where we left off, just in case it's pertinent, but I don't think it is: I did try checking timing not long after we got this sorted out a year ago, at the end of a trip, with warm engine, but was getting inconsistent results with each restart so I vowed to try again, and never got around to it (it ran fine with the switch unplugged, so it became a low priority).

The notes I have saved show it idling at +10 degrees, going to -26 when revving, then settling back at T when going back to idle with the switch plugged in.

With just the 12 degree switch unplugged (brown wire), it would idle at T, then jump to -10 at throttle crack, and move to -25 as you rev.

With both unplugged, it idles at +1 and jumps back to -26 when revving.

I've bench tested the throttle switch many times, and it always has proper continuity (when following the Suzuki manual that mphelle posted, or backwards when following my clymer manual - plugging it in backwards lets it idle fine, but then it dies as soon as you hit the 12 degree mark) so I don't see value in replacing it - the engine just doesn't like having it plugged in, but is happy as a clam without it.



NEW ISSUE:

This thing has been running like a champ for a year with it unplugged. Probably 150 gallons of fuel through it in that time. This past weekend, running fine as usual, then suddenly lost revs while running at WOT. Jumped down to somewhere in the 1/2 - 3/4 throttle range. A couple times jumped back and forth from WOT to that lower point (quickly, as if electrical connection was loose). It ran perfectly fine at that lower point (even if I left the throttle handle at full forward), and if I throttled back, had full control of everything below that point. Never shut down, never had a restart problem, but multiple times had the problem when running WOT. It seems that it's going into limp home mode.

It should be noted that this motor is not using oil injection. The tank and flow sensor were removed before I got the engine, so I removed the gear that drives the oil pump, and have been using premix. The coolant temperature sensor on top of #2 cyl has never been plugged in since I've owned it, either.

Since none of the oil and temp sensors are plugged in, my thoughts are the only 2 things left could be the low oil warning reset unit acting up and giving a false command, or the CDI itself (please not that again - had that issue with my last powerhead before swapping to this one). Easiest check would be to bypass the low oil reset, and try running it that way. My question is, is that done by just unplugging the two wires going into the CDI (Black with yellow stripe and Light green with black stripe), or does it require disconnecting everything? It seems it has wires going to the magneto as well, and I'm not sure if they should continue to pass through the reset unit, or be bridged straight to the CDI.