90 5.7L Merc with ThBt Ign. hard starts and stalls when throttled

[vipman]

Was running great all season then started to hesitate once you thottled it. Had to baby it up but once I got up the RPMs it continued to run smooth, but when I brought it back down to idle and then back up it would hesitate then sometimes stall. <br /><br />Got worst within hours to now it won't even start.<br /><br />Changed cap and roter and now I have to replace the starter because it failed from too much cranking I guess (all it does now is spin but won't actuate to flywheel).<br /><br />Check choke, seems to work fine, replace water separation filter and carb filter, tried timing buit still the same problem of not starting and when it finally did, stalling when throttling up. Also checked carb and it seems to be getting a steady flow of fuel.<br /><br />Any suggestions would be greatly appreciated because the starter is going to cost me $180 and I don't want to burn it up searching in the wrong places.<br /><br />Thanks in Advance and Sincerely,<br /><br />Allen afmnet@midwaynet.net

 

[elpaso]

Re: 90 5.7L Merc with ThBt Ign. hard starts and stalls when throttled

This site will help trouble shoot ignition.<br /><br /> http://www.marinemechanic.com/site/page251.html

 

[l1lmonsta23]

Re: 90 5.7L Merc with ThBt Ign. hard starts and stalls when throttled

You stated that you changed the cap and rotor, are you sure you are getting spark to your distributer? Your coil may have gone bad. If the motor sounds like it wants to start try leaning out your mixture, the sputter could be from it being to rich. Also, are your plugs black and smell like fuel?

 

[delkar]

Re: 90 5.7L Merc with ThBt Ign. hard starts and stalls when throttled

Hi,<br /><br />Have you checked the float level/condition in the carb. My 3.0 Mercruiser was doing exactly the same i.e. wouldn't idle and would only run if you kept pumping the throttle. turned out to be a shot float.

 

[Don S]

Re: 90 5.7L Merc with ThBt Ign. hard starts and stalls when throttled

If you have already done a tuneup and still have the problem, check the plug on the ignition module. It's located either on the distributor or on a plate on the exhaust riser. They get corroded and cause problems like that.

 

[waterone1@aol.com]

Re: 90 5.7L Merc with ThBt Ign. hard starts and stalls when throttled

This sounds like an accelerator pump that has failed (in the carb). With a helper at the contols and the engine off have them pump the throttle while you look down the throat of the carb. Do you see a jet of gas flow evertime they pump the throttle ? if not, your accelerator pump may be bad in the carburator.

 

[vipman]

Re: 90 5.7L Merc with ThBt Ign. hard starts and stalls when throttled

Thank you all for your replies.<br /><br />I did check the plug on the ignition module and disconnected the thottle linkage so I could pump the carb manually and yes there was fuel every time. <br /><br />I am going to check the coil and carb and hope that something turns up.<br /><br />Still baffled,<br /><br />Allen