OMC Cobra 4.3L - Very Hard to Cold Start

[coolguy982]

I'm new to boating and am learning as I go. Any help would be MUCH appreciated!

I just purchased a 1987 Thundercraft Citation 170 boat with a 4.3L OMC Cobra i/o motor. The boat is in great shape and was garaged its whole life. I've owned the boat for about a month now and have taken it out on the water a few times. If the boat sits for a week or so without being run, it has a very hard time starting up.

I just tried to start it tonight, and here's what happened:

1. I checked the battery. It was sitting right at 13 volts.

2. We hooked up the muffs, and started the motor. It cranked and turned over once, then died.

3. I tried to "pump" the motor as I read on some posts on this forum by moving the throttle back and forth a few times with the engine off. Tried to start it again and it cranked but wouldn't turn over.

4. Removed flame arrestor, opened butterfly valve with a screwdriver and sprayed starter fluid into the carb. Tried to start again, still cranked but wouldn't turn over.

5. Bro-in-law tried manually adjusting the throttle on the engine while I was cranking. Same results. To my knowledge, I don't think there is a way to increase the throttle while in neutral or choke the engine from the driver control panel (I don't see any choke buttons and I can't push the throttle forward or backwards without engaging it into gear first).

6. Measured battery again, now at 12.5 volts. Measured battery while cranking engine--10 volts.

7. Connected battery from truck via jumper cables thinking battery may be too low now. Tried to start, still cranked but wouldn't turn over, although it did sound like there was a little more power. Kept battery jumpered in for a while, then disconnected.

8. Tried to start again, this time while Bro-in-law pushed the butterfly valve in the carb open and closed repeatedly. The engine started to fire. It died a couple times, but then started up on the third or fourth. Bro-in-law was opening/closing butterfly repeatedly (maybe opening/closing twice per second).

We let the engine run for a while, engaged it in forward and reverse without problem, and then turned it back off. Tried starting it again and it started immediately. Did this about 4 more times and each time it started immediately.

Since it started up wonderfully while the engine was hot, we don't think the problem is the battery or plugs, or electrical for that matter. I don't see a choke button anywhere, so I'm guessing there is an electric choke somewhere? Since the engine wouldn't start until we opened/closed the butterfly valve repeatedly, does that mean some sort of air intake issue? As you can see in the photos below, the flame arrestor does have some oil buildup on the outside of it. Could this hinder with the air intake?

A couple other notes:

1. The butterfly valve was closed when engine was cold and does appear to be opening/closing properly when the engine is running.

2. The previous owner said that they would have to take off the flame arrestor and spray starter fluid down into the carb at the beginning of each season. That's why we tried #4 above.

3. We had this same problem the last time we took the boat out, but Bro-in-law that time toyed with the throttle on the engine by manually moving it in and out. We also had the butterfly open and had sprayed starter fluid down it.

4. Not sure if this is related or not, but after we finally got the engine started tonight, when I revved it up to 2000-2500 rpm and then put it back in neutral, the idle was at around 1600 rpm. Before revving it up (and just after starting), the idle speed was only about 950 rpm. It seemed that the throttle cable wasn't getting pushed all the way back when releasing the throttle. To fix this, we disconnected the red cable head in the third picture and turned it a few times. This seemed to do the trick and after doing this and revving it up to 2000+ rpm and back to neutral, it stayed at 950 rpm at idle.

Sorry for the long post, but I wanted to make sure I didn't forget anything.

Now, any ideas as to why the boat is having trouble cold starting?

Pictures of the engine are shown below:

 

[Bt Doctur]

Re: OMC Cobra 4.3L - Very Hard to Cold Start

If there is no button to push/pull for throttle only, try pulling the control handle outward and then foward.
dont rev it up on a hose, you will damage the impeller from lack of water
Throw away the ether, puts holes in piston tops.

 

[coolguy982]

Re: OMC Cobra 4.3L - Very Hard to Cold Start

I'll look at the throttle to see if I can pull it outward or not.

Thanks for the tip about not revving it up. When we revved it up, it only went up to 2500 rpm for 2-3 seconds and the rest of the time it was idling at 1600 or less. Do you think we might have harmed the impeller? Is the best way to tell just to see if the motor overheats?

 

[Gary H NC]

Re: OMC Cobra 4.3L - Very Hard to Cold Start

2500 probably did not hurt a thing.

The control should have a button in the middle that releases the handle for throttle only or at least pull out on the handle as BT Doc said.

Before starting advance the throttle full forward.This sets the choke.
Then while turning the key it may take a pump or two of the throttle to get it to fire.

It will not start in gear or at least is not supposed to.

If this is the black plastic OMC control the button in the center should have a rubber cap on it.

That flame arrestor looks like it needs a cleaning too...

 

[coolguy982]

Re: OMC Cobra 4.3L - Very Hard to Cold Start

Thanks for the reply. The only buttons on the throttle are Trim up/down and Tilt up/down, but I do not know if the handle itself can be pulled outward. I will try that tonight.

You are right that it will not start in gear. There is a stop button under the throttle handle that engages when it is in neutral. If I depress that stop button and push the throttle forward or backward (no matter whether I release the button or not) the gear is engaged, and the engine will not turn over at all (for safety reasons I assume).

I do not think it is an OMC throttle. I will snap some pictures if I can't pull it outwards.

 

[180shabah]

Re: OMC Cobra 4.3L - Very Hard to Cold Start

I will snap some pictures if I can't pull it outwards.

Pics would help, it has to have some method of disengaging the shift cable for warm up.

...Is the best way to tell just to see if the motor overheats?

Best way is to pull the impeller out and look at it, BEFORE it overheats. If the 2500 was brief, then probably no damage.


As noted above - ditch the starting fluid before you destroy your engine.

Idle of 950 is still to high by 250-300 rpm.
You choke is automatic, there is no button to activate it, moving the throttle handle also does not set it, but it will pump a couple of shots of raw gas through the carb - IF - the fuel bowls aren't empty. Did anybody check for fuel during all this cranking? Has you verified that the choke is set to manufacturer specs, it coulb befunctioning properly, but if misadjusted, it just wont work right.

Sounds like your two biggest problems right now are most likely, empty carb from sitting so long and not being able to advance the throttle while starting.

 

[coolguy982]

Re: OMC Cobra 4.3L - Very Hard to Cold Start

Best way is to pull the impeller out and look at it, BEFORE it overheats. If the 2500 was brief, then probably no damage.

To look at the impeller, I just take the top plate off of the outdrive, correct? I have an OMC Manual and that is what it looks like. Will I have to replace any gaskets if I just open it up to look?

Idle of 950 is still to high by 250-300 rpm.

My idle of 950 rpm is in neutral. When I shift into gear, I know it goes lower initially but I can't remember how much lower. I'm also just reading these numbers off the tach. Is the 650-700 rpm recommendation in neutral or in gear?

Did anybody check for fuel during all this cranking? Has you verified that the choke is set to manufacturer specs, it coulb befunctioning properly, but if misadjusted, it just wont work right.

We did not check for fuel in the fuel lines, but could smell gas through the carb throat. How do I go about checking the choke? Should that be in the manual? And can you point out exactly where the choke is (pictures in my manual are grainy)? Is this the round grey metal piece in my second picture just to the left of the carb throat and just underneath the left disconnected flame arrestor tube?

 

[cr2k]

Re: OMC Cobra 4.3L - Very Hard to Cold Start

Do you see good strong squirts of gas when you pump the throttle? If not your accelerator pump could be bad and need a carb O-haul.

Also put a volt meter on the + side of the coil. You should get 12v during cranking, if not your solenoid may be bad. Then try a jumper wire from the + battery post to the +coil terminal. if this works, you need a solenoid.

 

[coolguy982]

Re: OMC Cobra 4.3L - Very Hard to Cold Start

Thanks for suggesting to pull the throttle outwards! I did that last night and tried to start the boat again on the muffs. It started once and puttered out, so then I pulled the throttle out and pushed it up a bit and tried starting again. It worked that time!

Granted, it's only been 2 days since I last started and not 2 weeks like my previous first post, but hopefully this will help start it in the future!

 

[smarks]

Re: OMC Cobra 4.3L - Very Hard to Cold Start

Thanks for suggesting to pull the throttle outwards! I did that last night and tried to start the boat again on the muffs. It started once and puttered out, so then I pulled the throttle out and pushed it up a bit and tried starting again. It worked that time!

Granted, it's only been 2 days since I last started and not 2 weeks like my previous first post, but hopefully this will help start it in the future!

I have to pump mine 3 to four times before tunning key when she's been sitting for awile. After warm up all I have to do is turn key. Also, idel speed is suppose to be set in gear. If its starting good after warm up I would say that your carb is fine you just need to prime it a few squrts when cold.
Regards
Steve