Bogging down at high throttle

[prater]

My 85hp Chrysler runs great at idle in neutral, a little rough at idle in gear. When I punch the throttle it bogs down for a second then by the time I get to WOT it smooths out and runs great at WOT for about ten seconds, then bogs down to almost idle and dies and won't start right back up. If I then choke it, it starts and idles great again, same process starts all over. I replaced the fuel line (bulb included) two months ago, I'm considering tearing into the carbs, what do you think?

 

[tistore]

Re: Bogging down at high throttle

sounds like something clogging the fuel line...

 

[TwoFish]

Re: Bogging down at high throttle

You may have done this already but check compression, then spark & then move onto fuel. I've found this method helpful and it is suggested by more knowledgeable people on this site than me. It helps to isolate the problem.

Does the engine pick up if you have someone pumping the primer bulb?
Could be fuel pump needs a kit put through it.

 

[prater]

Re: Bogging down at high throttle

Compression and spark are good, first thing I checked. Should the primer bulb stay totally firm when running? It does not go flat, but isn't firm anymore when the engine is running. The line is a 3/8 which is too big for my connections (5/16) but its all the store had and I clamped it on really tight with hose clamps. Could it be sucking air. When I accelerate it has trouble through the mid range then clears up and runs great at WOT but only for about ten seconds till it dies. If I don't take it above idle, it starts, runs and can be restarted very easily as long as I don't accelerate much above idle. I went through the carbs last month. I'm thinking its the fuel line.

Also realized I've mistakenly been running the jets at 1 1/2 turns out from lightly seated instead of 1 1/4 turns out. Now I'm kind of nervous the engine may have been damaged from running lean.

 

[bman1bpm]

Re: Bogging down at high throttle

1 1/2 turns out is more rich than 1 1/4 turns.

It sounds like a fuel problem to me check all fuel lines. It doesn't really cost all that much to replace all of them, if they're original, I'd go ahead and spend the money on new ones. I elminated the quick connect on the front of my motor and just ran the fuel line directly to the pump.

While you're there, replace your gasket and diaphragm, it might be going bad or going bad. Also, place an inline fuel filter betweek your pump outlet, and the carbs, this will be a final filter to remove any junk that may have passed through the system before it plugs up your carbs.

When did you last service your carbs? They might be due for a cleaning, and most likely need to be synched up. The manual says how to do this, but there are probably better instructions on this forum if you search.

 

[prater]

Re: Bogging down at high throttle

Serviced carbs last month.

So the more I open the jets the richer the mixture gets! So could running rich be causing my problem?

I already plan to replace the main fuel line with the correct size (5/16) to see if this helps.

All the fuel lines on the engine were new in 2007. However I've been running without the breather box in place, could this be a problem?

 

[TwoFish]

Re: Bogging down at high throttle

I?m new to outboard repairs as well. So take what I say in that light.

The primer bulb on my boat doesn?t stay firm when running. It only stays firm whilst there is pressure built up between it and the carbys before the motor starts using petrol when started.

You may have covered these already.

New diaphragm for fuel pump. (cheap & easy to fit)

Replace old fuel filters . (inline and water separating if you have one) Depending on the year of your motor your fuel pump may have a filter screen in it.

Tighten all connections. I read somewhere about temporality using a clear section of fuel line between the carbies & the fuel filter or fuel pump (whichever is first) to see if there are any air bubbles getting into the system, to check for leaks. Need to be REALY careful running the motor with the cover off.

Check fuel tank is clean so nothing can block the pickup line. I once had a flake of paint from a filling can floating around in the tank. The motor would intermittently cut out at high speed. Took me a while to track it down.

Check the carbies again. Some good info in the FAQ on this site http://forums.iboats.com/forumdisplay.php?f=31

Hopefully someone else will have some ideas.

Good luck

 

[bman1bpm]

Re: Bogging down at high throttle

I operate my carbs wide open, I have the plastic covers for them, but for some reason I forget to put them on, they're just for looks I think, no filters or anything in them.

The fact that your motor requires choke to restart shows that you're running out of fuel. It needs the choke to bring some more gas into the carbs. How are your floats set? They should be parallel to the carb body when flipped upside down.

Also as previously mentioned...I'd replace the fuel pump diaphragm if you haven't already.

 

[prater]

Re: Bogging down at high throttle

So I replaced the fuel line today with a 5/16, much better fit. This time the motor did NOT want to start, would backfire every time I turned it. Finally got it running and it didn't want to idle low, would only run good if I opened up the jets really wide I mean like 2 1/2 turns open. Even then it was way too rich and wouldn't accelerate smoothly, usually died if I let it go too long. Pumping the primer bulb seemed to help. So I pulled the carbs off, soaking them overnight, tomorrow a new fuel pump diaphragm is going in as well. Any other ideas?

 

[67Johnson6HP]

Re: Bogging down at high throttle

Sounds like you are on the right track replacing the fuel pump diaphram and cleaning the carbs. Those tiny passages in the carb are difficult to clean - I take a twist tie and clean it down to the wire and run it in and out with solvent. I have had to re-clean carbs before. Also, make sure your fuel tank vent is open and not clogged. Good luck !

 

[capri1600]

Re: Bogging down at high throttle

How often do you get to run your boat? I have a Force 85 that has been sitting and used to pop once or twice while cranking for the first start from cold. Now that I have out a couple hours of runtime on this Fall, with fresh gas and Amsoil 100:1 Sabre oil mixed at 85:1, I barely touch the key w/choke and it starts and idles perfectly from a cold start.

Marty
http://www.martyhammersmith.com

 

[Frank Acampora]

Re: Bogging down at high throttle

A (tobacco) pipe cleaner will clean the small brass idle feed tube. I like to spray every passage with WD 40. Remove the idle needle and spray through that, noting that WD should come out all the small idle circuit holes in the top of the carb casting.

Remove the float and inlet needle. Thoroughly clean the inlet and elbow fittings, seat and needle. Be careful not to damage the seat and needle. If your carbs have the screw in seats, remove them to clean the inlet passage. Be certain there is no crap in the inlet which could intermittently clog the inlet needle and seat.

When you reassemble the carbs, invert them and using the center brass tab set the floats to be level with the casting. NOW, turn them right side up and using the stop tab at the back, set the DROP so the float almost touches the brass jet on the bottom of the casting. These two steps are critical as the float level determines how rich the carb runs and the float drop determines how much fuel gets into the carb. If these settings are not correct, no matter how you play with the needles, the engine will not run correctly. For example: If the float drop is not enough, the engine will idle but run out of fuel at high throttle settings. If the float level is too low, you will need to set the idle mixture needle way too rich and the engine will sag at speed.

If you have a quick-connect fitting at the tank, check it for partial clogging.

And, as always, buy and install a cheap plastic fuel filter between the fuel pump and carbs. This keeps pieces of a deteriorating diaphragm or possible broken button valves from cobbling up one or more carbs and causing engine damage. I like the ones with a fine screen in them rather than a paper element

 

[prater]

Re: Bogging down at high throttle

Thanks for all the replies, the carbs are off and soaking right now. A thunderstorm has moved in and I likely won't get to reassemble the motor today. Is it ok to leave the carbs off, holes open with the cowl on and tarp over the motor? Or should I put something over the carb holes?