Jump to content

Unofficial Home of Old Simplicity & Allis-Chalmers Garden Tractors

Sign in to follow this  
SMC17

620 Fuel Issue

Recommended Posts

SMC17
My 620 was losing power when mowing up hills and I noticed it was leaking gas from the fuel pump. Tightened up the pump and it regained power. It still seemed to slightly slow down the pto speed and deck when traveling up inclines so I decided to swap out the original pump for a electric one. After installing the electric pump per Dave's instructions on the site it started right up and I thought I was good to go. However after I started testing it under load it did several things. There was a presence of dark smoke on startup. It began losing power up inclines again, and it seemed to be weaker at full throttle. I tore down the electric pump and hooked up the mechanical pump again and it is back to decent operation and mowing. I can mow up inclines with only a slight power loss and it no longer has smoke at startup. However I'm now getting some after-fire after using it hard for 30 minutes or so. Any ideas as to why the electric pump is causing issues? I'm getting good return flow so it seems to be pumping correctly. Could my carb be out of adjustment to compensate for a weak pump and thus be overly rich using the electric one? Thanks, Sean

Share this post


Link to post
Share on other sites
JP
Sean, There is one 'elbow' that has a restrictor in it. It's supposed to be on the intake side of the carb from the pump. I think(?) it's there to 'smooth' out the pulsing from the mechanical pump. The 'free or unrestricted' elbow is on the return. When the float bowl is full, the float should shut the needle & the excess 'should' flow easily to the tank. So... Did you get the 'low volume' pump? Do you KNOW the elbows are in the right place? I'll be curious what others say about switching mech to elec pumps, I don't recall making any. Mostly just plug-n-play.

Share this post


Link to post
Share on other sites
SMC17
JP, I did not change the elbows around. I'm using the same return to the tank. I used a purolater low pressure pump 2.5 to 4 PSI. I also cleaned the air filter assembly before install.

Share this post


Link to post
Share on other sites
eagle5473
Sean, I dont know what would cause the difference in the 2 pumps, but what you describe sounds like you should double check the timming, I had same symtoms with the timming off

Share this post


Link to post
Share on other sites
SMC17
JP, the spark plugs aren't fouled. The spark seems o.k. I highly doubt that the elbows were switched but I can check that. The restrictor should be on the carb inlet regardless of what pump I use correct? Aaron, I thought about the timing but why would the 2 pumps cause the tractor to perform much differently? Noone thinks that it is a carb issue? I'll admit that when it comes to carburation and timing I'm a real novice. Sean

Share this post


Link to post
Share on other sites
JP
I was going to get to the timing also (Thanks Aaron!). A few things going on here... The carb AND timing could be off (Before the switch). Check the timing with a timing light to take it out of the equation. The electric pump will provide more & consistent pressure. IF the float & overflow to the tank are correct, I don't think it should matter. I would think if the float were off (too high), the new pump would fill the bowl faster(?). By the way, My 620 (Loader/backhoe) that I use ALL the time. Started doing the same thing! Tonight 'Alice' gets timing checked! LOL After that, she's usually happy! :D

Share this post


Link to post
Share on other sites
SMC17
Well it seems unanimous that I should check the timing/points/condenser so I'm going to try that this weekend. What still bothers me is why the performance of the engine was so different using the 2 different pumps.

Share this post


Link to post
Share on other sites
D-17_Dave
There are several things that could effect how the carb responds to the fuel flow. A pump, any pump, electric or mechanical, new or old can flow good when you open a line but falter when put under pressure. That being said don't take anything for granted as I've gotten bad pumps out of the box. Another issue I've seen is the needle on the float getting stopped up by small particles of rubber from a mech. pump diaphragm. As it breaks down it flows directly into the small needle passage way. I'd pull the carb. while you have it apart and look for this.

Share this post


Link to post
Share on other sites
Guest
This topic is now closed to further replies.
Sign in to follow this  

×