Rochester 2brl: Does this look normal? (Hole Shot Issues)

[egleas84]

Boat is a 1983 Stingray SVB165 w/ Mercruiser 120

I'm having issues with bogging on hole shot. When I drop the hammer it begins to accelerate, gets up to about 3500 then I have to have a passenger sit up front (if I have more than two) to plane her out. Once it gets up on plane and I tweak the trim I get ~4400 RPMS's @ 32 MPH (so I don't think compression is an issue).

Check out this video; I have two pretty solid streams dumping into the carb when I drop it all the way. So I think the accelerator pump is doing okay. Is it still possible the carb could be an issue with hole shots that aren't related to the accelerator pump?



I've already...
Removed the tank from the boat, dumped all old gas.
Put a full tank of fresh gas in with the corresponding amount of Seafoam.

I haven't...
Done anything with the filters
Tweaked any of the carb screws.

I changed the cap,rotor,wires and plugs today but wasnt able to splash it to test it; it starts runs idles the same as it did with the old ignition stuff; I didn't want to rev it too high out of the water with the cuffs.


One more thing; there is a flap (I think its a choke flap?) that doesnt seem to ever open or close (its always at least 70% open I never hear it shut when i turn the key on). Normal? Does it only close when the engine is cranking? It spring back open, but it seems like the spring is kinda weak.

 

[egleas84]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

14x19 SS. I know its 14" diameter, not 100% on the pitch, on the lower unit side of the prop it has 19 stamped on it. So its a safe bet

Posting pictures for fun:

 

[egleas84]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

..... (wet foam ?) unbalanced weight. Possibly a step down in prop pitch is needed. A 2" drop in pitch would bring WOT RPM's up to around 4600 RPM at WOT and give you more power out of the hole........

I hope its not foam... The way the boat is constructed I can't see under the deck without making a big hole. I'd rather try rebuild the carb and re-propping it before doing physical damage. In a different thread when this all got started I mentioned that when i bought it had sat with a 1/2 tank in it for 2 years, dont know if it was treated. then i topped off and went out. When i dumped the gas it was pretty hazy and had some interesting particulates in it. I guess what im trying to say is that I hope my carb is the problem. Restoring the floor is more costly and much more of a buzz kill. I'd do it though; love the boat style and so far the power package seems straight (exception of the carb maybe).

 

[90stingray]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

Haven't done anything with the filters??? That's a cheap easy thing to do and have it checked off your list.

 

[egleas84]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

Haven't done anything with the filters??? That's a cheap easy thing to do and have it checked off your list.

Yeah, I should have done it sooner. Have been planning to do it with the carb; figured if it's clogged a clean filter would mean nothing.

 

[egleas84]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

Another note on the foam: this gent is having the exact same issue; trusting that he took good care of it over the years it's probably not foam for him. We're both at the point of fuel system restores; should be interesting to see what both outcomes are. I didn't want to hijack his thread; so i created this one.

http://forums.iboats.com/showthread.php?t=469879&p=3178129#post3178129

 

[Vanover]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

couple things to consider IMO, rodchester carbs work a pretty much the same as other except the amount of moving parts inside. A steady stream of gas off idle does indicate that the acc. pump is working, when at idle you are on a closed idle circuit, assuming the choke is off and you are not on the fast idle circuit. After you give the initial burst of gas through the acc pump you are now on the off idle circuit taking fuel through the metering rods and fuel bowls. So when trying to figure out if you are running lean at a higher that normal RPM i would not consider the acc pump as a problem bc you dont stumble off idle. I doubt the problem is with the carb internals, if its not hard to start or flooded,(normally a needle and seat in this app). you could however opt for a rebuild, regardless it will help overall performance. Funny things happen to this style of carb. I run multiple see through filters so i know i am getting good clean gas. IF you suspect that dirty gas has passed into the carb, these are among the worst( tons of small passages) get it or do it yourself rebuild. As for the top butterfly valve, without more details as to man or elec choke i would guess its choke, and yes should be @ a 90 deg angle to the carb when full open, and yes that will affect top end perf if its open 3/4 as opposed to full. Hope this helps. Not a pro by any means but have been elbow deep in this type of carb for the last 10 or so years. on a side note 4400 rpms is pretty good for a boat of your size with your combo. Could very well be overweight as mentioned above.

 

[egleas84]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

What if that choke flap is getting sucked shut (parallel to carb) when I drop the hammer @ hole shot? it moves freely unless it's being actuated shut (electronic choke), the only thing that keeps it open is that spring which doest do a good job (I can push it shut with my hand and it stays...) Maybe not all the way shut but enough to mess it up. When I changed my plugs they had quiet a bit of unburnt gas on them even after a day or so, is that normal? Or could I be running partially flooded/very rich and blowing gas out my exhaust at hole shot/cruise speed.

Speculation; but that flap concerns me until I understand how it's supposed to work.

 

[dan t.]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

Make sure the choke is opening fully, unless you are running in the winter you dont even need a choke, tie it open and just pump the gas 2 or 3 times for initial start up.

 

[81 Checkmate]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

Like Dan T said. I would tie the choke flap open to see if thats the problem. If you are concerned about start up, start as nomal then when to temps pull cover off then zip tie flap and try.

 

[egleas84]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

Is the throttle linkage supposed to control its % open or does the electronic side of things do it? I just had this sucker rebuilt and I almost think he connected the linkage wrong. This is at WOT. The butterfly is shut; so if the electronic doesn't control it its backwards.

 

[dccordell]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

If that is setup like my 2bbl rochester (even though a different motor), the choke is electric (I can see the choke coil "box" on the other side of the carb, it's the round black thing that the shaft of the choke valve goes into, and should have two wires hooked into it). The choke is operated from the ignition switch. When the Ignition is off, the coil spring that moves the choke is retracted, closing the choke (as in your pic above). When the ignition switch is turned on, power is supplied to the choke spring causing it to heat up (inside that little round black box) and as it heats it will expand and allow the choke valve to open up. I'm not sure how long it takes for it to open all the way but it's not very long (couple minutes at most?)... it will slowly open as the spring heats up.

It looks like your choke isn't opening, or it's not opening all the way. In your picture above, the choke should be closed (as it is) because you probably didn't have the ignition switch on or if you did, it probably hadn't heated up the choke spring yet.

The choke can be adjusted so that it will open all the way once the coil has heated up. On that black round "box" I mentioned earlier (on the top rear of the carb), there are 3 phillips screws. Loosen those and you can rotate the spring CW or CCW so that it will close or open more. The service manual goes over how to adjust it properly. If the choke doesn't open all the way, it obviously will restrict the needed air flow to run at WOT.

Hope that helps! Check your wires to the choke, make sure they give the choke 12v the entire time the ignition is on.

 

[egleas84]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

If that is setup like my 2bbl rochester (even though a different motor), the choke is electric (I can see the choke coil "box" on the other side of the carb, it's the round black thing that the shaft of the choke valve goes into, and should have two wires hooked into it). The choke is operated from the ignition switch. When the Ignition is off, the coil spring that moves the choke is retracted, closing the choke (as in your pic above). When the ignition switch is turned on, power is supplied to the choke spring causing it to heat up (inside that little round black box) and as it heats it will expand and allow the choke valve to open up. I'm not sure how long it takes for it to open all the way but it's not very long (couple minutes at most?)... it will slowly open as the spring heats up.

It looks like your choke isn't opening, or it's not opening all the way. In your picture above, the choke should be closed (as it is) because you probably didn't have the ignition switch on or if you did, it probably hadn't heated up the choke spring yet.

The choke can be adjusted so that it will open all the way once the coil has heated up. On that black round "box" I mentioned earlier (on the top rear of the carb), there are 3 phillips screws. Loosen those and you can rotate the spring CW or CCW so that it will close or open more. The service manual goes over how to adjust it properly. If the choke doesn't open all the way, it obviously will restrict the needed air flow to run at WOT.

Hope that helps! Check your wires to the choke, make sure they give the choke 12v the entire time the ignition is on.

Awesome info! Exactly what I was looking for. I did not have the ignition on; but now I know how to check if it is indeed operating properly and try adjusting it (I found the part of the manual you spoke of).

I should only have to turn on the ignition right and not actually start it up? In which case; is it a problem (for testing) to leave the ignition on (with the OIL light illuminated)? I imagine if I left it on then actually tried to cold start it I'd have a lot of trouble because the spring would have heated and opened, right?

Am I going to blow myself up if I startup without the flame arrestor on (cuffed in the driveway) to observe the carb while running? "Flame arrestor" has a lot of implications...

 

[egleas84]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

Ran out to the garage and tried it with the key on. Works exactly like you outlined, went WOT and it kicked it open even more than the spring did. One less thing to worry about! Case closed on the choke. Thanks!

 

[haulnazz15]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

There's no problem in running the carb without a flame arrestor for diagnosis, it mainly there for backfires through the carb. Just make sure you are running your blower.

 

[LilRedNeckGirl]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

Wait a sec, you hit apx 3500 rpm, and your not up on plane? then you have to have someone move up front to get on plane... then everything is fine short a few rpm on the top end....
First check the basic angle that your engine is at. If its too far down/ like almost under the boat, it will nose dive you, if its to far up, /away from the transom, your pushing water up behind the boat, pushing the transom down, and will have one dickens of a time getting on a level plane. sounds to me like a trim issue. Are you using trim tabs....

 

[egleas84]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

A new prop fixed my trim issues. Planes easy now with a genuine Merc prop

 

[dccordell]

Re: Rochester 2brl: Does this look normal? (Hole Shot Issues)

Sounds like you got it all straightened out... now the good times begin!!