Throttle trouble

[1979BumbleBee]

I have a 1979 Johnson 150. I took it to the lake for the first time after buying it. It took a while to start up but once I got it running I took it out. I noticed that after I eased it to full throttle that I was only going 10mph. I figured it just needed to warm up but it wouldn't go faster when I went full throttle. After running it for 10 minutes in full throttle, it suddenly kicked in and hit 30+mph. Then i throttled down to slow down then it immediately went back to 10mph. I started slamming the throttle down and you could hear the engine roar for a second like it was gonna take off then it never did and only went 10mph. How can I fix this?

 

[ThomW]

What were the RPM's at when you were going 10 mph? What about when it jumped up to 30 mph? When you are going along and only able to go 10 mph, if you press in choke quick, does it give a temporary boost? I would guess its either a gas issue, or spark. Have you checked to see if you have spark on all cylinders?

 

[Bondo]

Ayuh,..... Sounds more like the motor ain't runnin' right, Vs: the throttle not workin',....

Check the fuel filters for crud,...

 

[1979BumbleBee]

What were the RPM's at when you were going 10 mph? What about when it jumped up to 30 mph? When you are going along and only able to go 10 mph, if you press in choke quick, does it give a temporary boost? I would guess its either a gas issue, or spark. Have you checked to see if you have spark on all cylinders?

At 10mph I was pushing 6-7 rpms and when I pushed it it was still 6-7 rpms

 

[ThomW]

Just to be clear, what do you mean 6-7 rpm's? 600-700? 6000-7000? You did try pushing choke in, with no boost in acceleration? When was the last time the carb was cleaned/taken apart? As Bondo said, have you checked the condition of any in line fuel filters? If you are getting 6000-7000 rpm's, I would think you are getting enough gas. If you are running 6000-7000 rpm's, then you might have a prop hub slipping. 6000 rpm's is really spinning to only be going 10mph, if it stays at 6000 rpm's when it jumped up to 30 mph, check for a spun prop hub. Let us know what you have found out!