GT40 Surging and Top End
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Boat Maintenance
Forum Discription: Discuss maintenance of your Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=39147
Printed Date: November-16-2024 at 3:37pm
Topic: GT40 Surging and Top End
Posted By: mnfazer
Subject: GT40 Surging and Top End
Date Posted: June-29-2016 at 6:11pm
| I have a question regarding some performance of my '95 Super Sport with the GT40. At times is starts and runs perfect, but the speed tops out at 35 mph and it almost seems to be missing a little bit. It has a 644 prop but that shouldn't affect the top end much... Another time after starting it, it would surge really bad when I engaged the throttle. If I shut it down and started this would often clear that issue. Any ideas on what would cause this? Could it be the Oil Pressure Switch, HPFP, Fuel Filter...... Thanks much! |
Replies:
Posted By: MrMcD
Date Posted: June-29-2016 at 6:52pm
|
When I first purchased my 95 after it had sat in a garage for nearly 20 years, (100 hours in 20 years) it had a similar issue. It was winter and I had time to play so I changed the impeller on the water pump, I had seen some temp variation although no overheat. I changed the cooling temp sensor that sends information to the computer and the oil pressure sender that sends a signal to the computer, not the one that powers your oil pressure gauge. I changed the Fuel filter and tightened all the hose clamps on the raw water intake system from the boat bottom to the raw water pump to make sure it was not sucking air. Also had to fix the seal in the water strainer. Last I cleaned the connections on the lanyard that plugs into the gear shift /throttle control, this is the safety kill switch that can kill the engine if you pull it out. I just made sure it was clean and put a little electrical lube on the contacts. Since I did all this at once and the problem has not come back in 2 years I know one of the above got me back running well. It has not missed a beat since. I believe there is a thread on this site that addresses the GT 40 and common issues they have. Be worth it to read what it says. |
Posted By: mnfazer
Date Posted: June-30-2016 at 11:00am
| Thanks so much for the reply. I did change the impeller this spring and the temp is spot on at 160. I will look into the sensors and fuel filter. I borrowed a fuel pressure gauge so I can check that it is at 40psi. I will probably get around to new plugs, wires, distributor as well... |
Posted By: tryathlete
Date Posted: June-30-2016 at 12:32pm
|
I think you'll solve this quickly by doing proper troubleshooting and not tossing parts at it. Top speed of 35 with a GT40 and an Acme 644 should be at least 44-46. Take your time and verify each system. I'd look at fuel first. It seems a lot of us have found issues with the LPP and FCC. Get a pressure gauge and install it and eyeball it while running and watch for needle jumping. |
Posted By: mnfazer
Date Posted: June-30-2016 at 12:37pm
| Ok thanks for that. What is the psi supposed to be on the LPP? Also I was under the assumption that the 95' SS with GT40 did not have an FCC. I am wrong on that?? |
Posted By: tryathlete
Date Posted: June-30-2016 at 2:20pm
| You are correct. No FCC. LPP fuel pressure is something like 6psi but the pressure you're reading off of the Shrader valve is 40psi and steady. I don't know where you'd read LPP just never did it. I had massive variations at the Shrader so I replaced LPP and all was good in my case. |
Posted By: gun-driver
Date Posted: June-30-2016 at 11:49pm
During crank 39+/- 3psi Idle 31+/- 3 psi WOT 39 +/- 3 psi Go to the reference section there is a manual section go to the bottom and there is a GT-40 manual. There is a section on theory of operation 2A-17 it will help you understand how things work |
tryathlete wrote: