DT75 - can't get it to stay running

[Gas Giant]

Re: DT75 - can't get it to stay running

I'll try to run those tests this evening, but it might have to wait until Sunday. I agree that it is a fuel delivery problem - just need to identify what the specific problem is. (easier said than done, it seems!)

I'm also going to pick up one of those gallon jugs of carb cleaner, and I'll use the carb cleaner in the ultrasonic cleaner and hopefully they come clean that way. I've used those jugs in the past on car projects; in fact I think I still have an old jug but its probably got more junk in it than my carbs.

I'm not really sure how I would remove the broken pilot jets; it looks like they were intended to be removed with a flathead screwdriver or similar tool, but half of the "screw head" has broken off. (Looks like someone tried to remove them at some point.....)

I HAD to remove them, I could take them to our machinist at work who could probably get them out somehow. If it isn't completely necessary, I'd rather not bother him.

 

[waffles1]

Re: DT75 - can't get it to stay running

Gas Giant,
Those jets need to be removed and replaced with new ones. If you had these carbs rebuilt they should have told you they needed to be replace. Check your manual but I believe the settings for each are 11/2 turns out from lightly seated. I would start there before I did anything else. That could be your whole problem. Good luck!!!

 

[Gas Giant]

Re: DT75 - can't get it to stay running

waffles1, I tried them at 1 1/2 out, and 1 3/4 out, and 2 out, the engine always behaved the same. Its almost like I have a ghost shutting it off.

The machinist left for the day, and I don't think he works tomorrow, but I can try and extract them myself over the weekend.

 

[99yam40]

Re: DT75 - can't get it to stay running

How in the world did you try them at the different settings if they are broke off?

 

[Gas Giant]

Re: DT75 - can't get it to stay running

The idle air screws are what I tried to adjust - the pilot jets are what are stuck.

 

[mphelle8vld]

Re: DT75 - can't get it to stay running

I've been following this post and when I read that you had first installed the primer bulb backwards, I thought like others that maybe you just weren't getting the carbs cleaned.

Suzuki cdi's from that period automatically advance the timing 10 degrees for only 15 seconds to aid in starting, and then revert to the idle speed adjusting switch on the front of your motor. The fast setting on that switch is 0 TDC but if your switch is bad (open) the timing would be set at 6 ATDC which might be causing your motor to die. You could test the switch, the fast setting should read a short, or just try the next slower setting which should be 2 ATDC. I believe you need to return the start switch to the off position each time to reset the cdi, in order to get that initial 10 degree advance on start up.

 

[Gas Giant]

Re: DT75 - can't get it to stay running

mphelle8vld - I haven't heard that before, that is very interesting. Definitely a new thing to check, and I was wondering if there was some electronic wizardry happening behind the scenes. I'll whip out the digital multimeter and post what I find.

Either way, I am definitely dunking the carbs in a bucket of carb cleaner and soaking them for a bit. If I can get permission to bring the ultrasonic cleaner home I will put the carb cleaner and carbs in that; but that won't happen until next weekend at the earliest.

I also noticed that in the Clymers manual, the pilot jets are referred to as pilot (idle) jets - so I am definitely finding a way to extract my broken ones and replace them. I'll probably order some new ones from Brownspoint Sunday or Monday.

I'd also like to take the time to thank everyone for helping so far; I've learned a whole lot in a short time. I suppose in the end all this frustration will be worth it, because I will know this engine backwards and forwards.

 

[waffles1]

Re: DT75 - can't get it to stay running

Sorry gas Giant I misunderstood you. Did you pull out the air screw jets and clean them and passages where they go?

 

[Gas Giant]

Re: DT75 - can't get it to stay running

Waffles1, yes. Those turned easily, but the pilot jets are pretty well stuck in place. Well, at least until they make me mad enough.

 

[99yam40]

Re: DT75 - can't get it to stay running

You really need to remover those screws and all other parts from the carbs when cleaning to make sure you clean all passages and the readjust as the manual states

I also miss understood you, I thought you had broke off idle mix screws.
The jets being stuck may not be that bad if the orifices are still the proper diameter and there is no restriction.
Just easier to clean properly if all parts are removed when cleaning.

Did you fix the fuel leaking out of the top carb and where ever else it was leaking?

 

[Gas Giant]

Re: DT75 - can't get it to stay running

Slight update: (I didn't want to work on it too much today; I didn't want to get mad at the end of a good weekend )

I tested the fuel pump by having it squirt fuel into an empty beer bottle. It seems to be pumping fuel just fine.

I also tested the throttle valve sensor by hooking it up to a digital multimeter per the Clymers manual. The voltages at full closed and full open were within spec and didn't require adjustment.

That's all for now; I am going to try to drag the ultrasonic cleaner home tomorrow and try my hand at cleaning a carb that way.


One more thing - I just noticed a disconnect between the Clymers manual and the green Suzuki Outboard Motor Service Manual. The Clymers manual calls for a float height of 0.39-0.47 in, where the Suzuki Outboard Motor Service Manual calls for a float height of 0.69-0.77. That is quite a difference - I went with the Clymer's manual because that is what I had with me at the time.

Does anyone have any thoughts on what the float height should be for these carbs?

 

[stylesabu]

Re: DT75 - can't get it to stay running

i have a 82 suzuki, dt75 factory manual and a complete spare motor. I'll look up float spec tomorrow.

 

[stylesabu]

Re: DT75 - can't get it to stay running

spec is .69- .77" with carbs turned upside down see pics

 

[Gas Giant]

Re: DT75 - can't get it to stay running

I have that manual too - I have found that setting the floats to that height is a physical impossibility! The float hits the carb body around 0.67"

In other news, ran them all the carbs through the ultrasonic cleaner. I managed to get the main jet and nozzle out of the bottom carb - most of the holes in the nozzle were plugged up with crud, and crud came out of some of the passages when I blew them out with compressed air. So that was definitely a problem with the bottom carb.

The middle carb is still a problem. I noticed that not even compressed air is freeing up the passage between the main nozzle and one of the holes at the top of the carb. (On the other two, water and air were able to flow freely though this hole.) I can't for the life of me get the main nozzle and jet to come loose - it looks like someone has tried it before due to damage to the hex, and I added to that damage. They need to come out because I believe they are plugged and crudded up like the bottom carb was.....so I am going to take the carb to the machinist at work Monday and see if he can extract the nozzle and jet. Obviously they are going to have to get replaced.

So, its looking good as far my problem being carb related. I wish I hadn't destroyed the evidence of the uncleaned carbs - I don't think the middle and bottom one ever got touched - I would have considered taking the mechanic to small claims court to get my money back since its fairly obvious he didn't do what I paid him to. I didn't think of it until it was too late, so oh well.

 

[James R]

Re: DT75 - can't get it to stay running

On my earlier reply I suggested using Gunk Carb and Parts cleaner.
Did you use it?
If not, you should try it before going to more expense.
You will be impressed.

 

[99yam40]

Re: DT75 - can't get it to stay running

I would still have a chat with your mechanic about it to see what he has to say, or better the owner of the shop if they are different people.

 

[Numlaar]

Re: DT75 - can't get it to stay running

Gas Giant,
Those jets need to be removed and replaced with new ones. If you had these carbs rebuilt they should have told you they needed to be replace. Check your manual but I believe the settings for each are 11/2 turns out from lightly seated. I would start there before I did anything else. That could be your whole problem. Good luck!!!

+1 Lean/Rich settings very touchy

The idle air screws are what I tried to adjust - the pilot jets are what are stuck.

Not to doubt you, but I have seen where some people count turns as one revolution of the screwdriver blade, thats actually a half a turn of the screw... Just want to be sure, you have turned the screw out completely one full and one half revolution.... (which would be 5 turns of the screwdriver blade).

I have the DT115 (basically same motor with 1 extra cyl/carb)... From everything I have been through with my fuel system, I can concur, these are some VERY sensitive carbs... I had a very similar problem with mine starting/idling after a rebuild, and it was all due to the lean/rich settings... once I got that right, it has run smooth since.

 

[Gas Giant]

Re: DT75 - can't get it to stay running

Numlar - yes, I was careful about that; I made that mistake on a Q-jet in my teenage years. Its something that is easy to misinterpret or make a mistake on.

James R - that was going to be my next step. However, a new development has arisen. In trying to extract a fubar-ed main jet from the middle carb, I actually cracked the carb body.

So, I am hopefully going to be picking up a set of carbs for sale locally. I'll give them a good inspection to make sure I'm not starting from square one again, and I'll throw in a rebuild kit before I install them.

Both the middle and bottom carbs (the ones I have been working on, not the new ones) had the main jets completely plugged with varnish and this weird white/green powdery junk. No idea what happened to these carbs in their past life with their previous owner, but it certainly wasn't good.

When I get the replacement carbs installed, I'll again test fire the engine and let you guys know what happens.

 

[James R]

Re: DT75 - can't get it to stay running

Salt water and salt air and leaving the carbs with no fuel in them can and does cause the issue that you see. Be sure to use Stabil and don't allow the carbs to go dry.
I have some junk carbs here from a Suzuki that were put to that test. Replaced the carbs with a used fresh water set and no more problems.
Pleased to see you finally found the problem.

 

[99yam40]

Re: DT75 - can't get it to stay running

Both the middle and bottom carbs (the ones I have been working on, not the new ones) had the main jets completely plugged with varnish and this weird white/green powdery junk. No idea what happened to these carbs in their past life with their previous owner, but it certainly wasn't good.

you paid someone to clean these carbs several times and you cleaned them yourself a couple of times and you are still finding all this?