Will no longer hit top speed

chapron67

Member
My Amphicar has recently been fully and professionally restored (700 miles now) on it. It runs perfectly expect it will no longer 'hit' top speed. I use to be able to drive it, on the flat, with 2 adults at 65-70 (with a little left -- and yes, I varied the speed as I was breaking in the engine) but now it'll only go 50. It doesn't smoke, starts and idle perfectly, rev's up fine, etc.

I've checked the fuel filter, cleaned the fuel pump (checked pressure as well), checked carb (throttle is wide open with gas pedal is down all the way), cleaned main jet. Checked that each cylinder is firing (by removing the spark plug wire and seeing if it 'stumbled' (which each did).

Appreciate any idea/ thoughts/ things to check!

Thanks!

Greg
 

mike_israel

Amphicar Forum Admin
Staff member
Greg,

I do not have the answer but I experienced the same thing.

After my Amphi was restored (engine and tranny both rebuilt), it has been noticeably slower than when she was old and leaking oil. I too could cruise down the AC expressway at 70 and now feel like she runs out of steam just above 50. She runs perfectly, starts right up, idles great, just slower than before.

Mike
 

Tedredamphi

Platinum Subscriber
Check your vacuum advance unit for proper operation. Timing should advance as you run the RPM up on the engine. Could be vacuum hose from carburetor or the vacuum unit itself.
Ted
 

Bilgemaster

Member
My Amphi could hit 70 if you threw it outta the space shuttle.
Otherwise, it likes cruising in the flats at about 58. On the
interstates I'd just run with the trucks.

Regards,
Bilgey

On Mon, Oct 18, 2010 1:25 pm, mike_israel wrote:

> Greg,
>
> I do not have the answer but I experienced the same thing.
>
> After my Amphi was restored (engine and tranny both rebuilt), it has
> been noticeably slower than when she was old and leaking oil. I too
> could cruise down the AC expressway at 70 and now feel like she runs
> out of steam just above 50. She runs perfectly, starts right up, idles
> great, just slower than before.
>
> Mike
>
>
 

azpaul50

Member
I'm really surprised to hear this. I made 55 on the flat towing a tear drop trailer with a Harley scooter behind it. I must admit it took a while at full throttle to get there. A head wind slowed me down considerably on the way home to like 35. Without the trailer it'll do 70 MPH easy but until I get my brakes right, I'm not doing much of that. I wonder if Tommy in Tampa did something to the engine? It's got a blue valve cover instead of copper. It's been sitting since May but I may have it out this weekend maybe just towing the scooter. Blub, which I sold, had a strong engine but the handling was shakey above 50 but the legs were there. Who'da thought an Amphi might lose a land race with a Messerschmitt?? - AZP



To: azpaul50@hotmail.com
Subject: RE: [General Amphicar Discussion-t-20915] Re: Will no longer hit top speed
Date: Mon, 18 Oct 2010 15:57:41 -0400
From:





My Amphi could hit 70 if you threw it outta the space shuttle.
Otherwise, it likes cruising in the flats at about 58. On the
interstates I'd just run with the trucks.

Regards,
Bilgey

On Mon, Oct 18, 2010 1:25 pm, mike_israel wrote:



Quote:




> Greg,
>
> I do not have the answer but I experienced the same thing.
>
> After my Amphi was restored (engine and tranny both rebuilt), it has
> been noticeably slower than when she was old and leaking oil. I too
> could cruise down the AC expressway at 70 and now feel like she runs
> out of steam just above 50. She runs perfectly, starts right up, idles
> great, just slower than before.
>
> Mike
>
>
 

chapron67

Member
>>>>>Check your vacuum advance unit for proper operation. Timing should advance as you run the RPM up on the engine. Could be vacuum hose from carburetor or the vacuum unit itself.

would you expect the engine to be missing/ running poorly as the timing would be off if no vacuum, or just less 'power' (the car currently runs perfectly at full throttle, just lost 20 mph some how...) without a functioning vacuum advance. The car has electronic ignition.

g
 

jfriese

Active Member
Before I upgraded my Amphicars to 1296 engines my cars ran fine at 70 MPH on the flats but slowed down with the slightest uphill grade. I doubt the vacuum advance (which is actually a retard on the Amphicars) is at fault but the centrifugal advance might be the problem. Put a timing light on the engine and check to see if the advance is working properly. By 3500 RPM I would expect about a 20 degree advance from whatever the advance is at idle. Also be sure that one of your brake shoes isn't stuck in the engaged position. A stuck brake will definitely slow the car down but if it were on tight enough to slow the care down that much I think that brake would start to smoke before you went too far.

P.S. With a 1296 engine my Amphicars easily do 85 MPH and they have plenty of room under the gas pedal at 70 MPH. If everything is adjusted and working right, the cars are very stable at whatever speed you run them at. Be sure your front tires aren't inflated too much. I run the front tires at 14 PSI with bias ply tires and about 20 PSI with radials.

John Friese
67 White
67 Red
 

Midwest Amphicar

Worlds Largest Amphicar Destination
Change your oil. Dump in clean pan. Look for anything besides oil. tight bearings will slow you down. Later Dave
 

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