Blackmax 135 v6 1986 no power on low revs

[UKMike]

Hi all,

I have just rebuilt motor after snapping the main steering arm and as a result of this damage I decided to replace the lower unit bearings, added a new exhaust plate and a carb rebuild, but since getting her back together she's not running right. The lower unit seems smooth and the engine runs OK on idle, but when I took her out onto the water she was not running right and felt as though she was either flooding or being starved of fuel. Now I checked all the connections fuel wise and they are all correct, I also added new bleed valves and pipes while she was in pieces (one at a time) and also added the bleed restrictors called up on Service Bulletin p/n 823829. The problem I am seeing is that on idle and not in drive she seems to run smoothly, a little lumpy but nothing out of the ordinary, but when I put her in the water and put her in drive she feels as though something is knocking (about 1500-2500 revs approximately, or the best way I can describe it is like one or two of the cylinders are not firing or that they are flooded, I say this because if I start moving forward I get to about 2200 revs and the engine is clearly not firing correctly and when I push the throttle forward all the way nothing happens and she holds back, she gradually builds up speed until the revs pickup enough to engage the main jets and all of a sudden she bursts forward and runs perfectly.

Does anyone have any thoughts on this?

I can show her running in idle if you want to see what I mean, she really is quite smooth on idle, probably more so than ever before..

 

[UKMike]

Do you think this is likely to be the fuel pump or float adjustment or possibly fuel filter? She was running great before the power head was split from the mid section and of course before the carbs were rebuilt.

 

[Chris1956]

A leaking fuel pump will cause a cylinder or two to load up with raw fuel. I would check/rebuild it.

After you eliminate that as an issue, if she still loads up, remove the spark plugs and see if you can tell which ones are fouled. You can then trace it back to the misadjusted carb barrel.

Also, if any spark plugs are real clean, you could be getting water.

 

[UKMike]

Thanks for that Chris, I really appreciate your reply, I actually needed to remove the fuel pump in order to get the main petrol supply back onto carb 1, I wonder if that was the cause... Also I checked the plugs and plug 3 was spotless, like brand new but to be honest I don't understand how lifting the power head and replacing the exhaust plate could cause that, I know all the plugs were running a normal colour before the changes. I also cleaned the plugs spotless before making the changes so it's hard to know if that is an additional issue. After running her for the first time after the changes all plugs were really wet and black except plug 3 which suggested non firing or other but it was slightly wet with fuel not water after a 5 minute run on idle. I didn't split the head or anything like that, All that was done was power head lifted and a new plate installed, gaskets scraped and replaced with sealant below power head only with the addition of new exhaust gaskets, exhaust cleaned and checked.

 

[UKMike]

Would love some help here

 

[Chris1956]

Mike, I am not an expert on the V6 motors. However, from the engine block diaghram, it appears that the exhaust divider plate, could leak water into a cylinder, past the gasket I would therefore watch your spark plug colors, to make sure they get to be brown. If they stay clean, maybe you have a water leak....

 

[Dukedog]

don't think he remover tha divider.. think hes talkin' adapter plates... type and amount of "sealant used on this part?.. when ya did tha carbs did you use all new gaskets inside and out?.. this is a "must"... get floats set right?.. change any adjustments on any of tha linkages?.. do tha fuel pump?.. checked fire on all six?.. all bleed lines good and routed as should be?.. tha carb idle circuit drops out tha instant you apply "any" movement to tha throttle at all.. low side of stator could also be a culprit..... justa a "few things" ta keep ya busy.

 

[UKMike]

Hi Chris,

Thanks for that, I can't see anywhere that water could get in, the exhaust plate holds the engine mounts on top and the exhaust below and there is another plate on top of that to seal the unit before it connects to the powerhead and there is a gasket between that top plate as well. If water could get into the end cap I guess water would get into the crank but if that happened I would assume it would get into all cylinders and not one specific piston.... I'm not sure though. thanks for the thinking...

 

[UKMike]

Hi Dukedog,

Thanks for the input, and yes the adapter plate that holds the upper engine mounts. the new gaskets were all put on dry except the lower powerhead gasket, the one that seals the powerhead to the top plate, right under the end cap and it was proper blue gasket sealant on both sides of the gasket to seal it properly as the engine relies on a perfect seal there for back pressure.

Yes the carbs were totally rebuilt with the full kit, the only thing that wasn't changed was the idle needles, although I did try to set the carbs at 1.6mm hang it's very difficult to set them at that level and some may well not be right, and if they are wrong they are not shutting off early enough as they would be set to high. all same linkages and all set to open the butterflys at the same time. Yes all bleeds were done one at a time and replaced the pipes with new but inserted restricters. It does fire on all six and if the idle drops after any movement on the throttle it would suggest it is a flooding issue as it wasn't trying to stop, it was trying to gradually increase revs. The stator and trigger were new last year and had about 6 hrs of use, also new ignition modules, full harness and coils last year.

I did take the fuel pump off as I couldn't get the fuel supply onto carb 1 and I couldn't remember which of the 4 bolts to undo on the pump so undid them all, which opened up the pump. As soon as I remembered which bolts I needed to remove I screwed the other bolts back. It's probably that now I think of it.....

Thanks again all for your help, much appreciated

 

[444]

Did you do a link and sync as per the factory manuals? When I bought mine it would idle great at idle but wouldn't get past 1500 rpm. I pulled the carbs, cleaned them, put the boat back in the water and still no dice. Finally did the link and sync following the instructions in my manual and after that I had all the power.

 

[Dukedog]

you say you "rebuilt motor"?.. what did that include?

to set floats hold tha bowl upside down and level... floats should be set to level hangin' with bowl level.... you mean float needles and seats hopefully... if you changed nothin electrical and didn't move any linkages and/or timin' screws since it was runnin' right, firin' on all six then it almost has ta be something fuel related.... carbs/fuel pump.. might check enrichner soleniod....

 

[UKMike]

Thanks all, yes when I say rebuilt motor it's a loose term as didn't rebuild powerhead, only the rest of the engine and the carbs.Yes I changed the float needles and seats but I didn't change the big long needles that have a couple of pinholes in them, they stick up in front of the butterflys. And didn't change any electrical parts or even any earth or ground points. Power head was lifted up in one movement, separated at the choke plate. So will put a new fuel pump kit on and rebalance the floats, thanks for all the help and advice, very much appreciated.