115hp 1974 cranking issues

[VTX1300]

I just rebuilt the powerhead with forged pistons,chrome moly rings ect...
The motor is hard starting. I have to sprayfuel in the throat to get it to start but it still takes a few turns before it pops off. Then it is fine runs great. Replaced fuel pump and rebuilt the carbs. I thought it was a fuel issue but second guessing it. It seems like it has a weak spark to no spark untill you crank it a few times around on all cylinders. I am guessing it might be the powerpack may be weak. Any thoughts on this?
Thanks
Rich

 

[CharlieB]

Re: 115hp 1974 cranking issues

A weak powerpak could make a motor hard to start but your should notice a weak spark usually exhibits itself as a high speed rpm limiter.

Faulty fuel enrichment, choke failing, slow cranking speed, weak battery or worn starter, possibly weak magnets could all contribute to hard starting.

Keeping with the K.I.S.S. principle, start with the easiest

 

[VTX1300]

Re: 115hp 1974 cranking issues

It has a very weak spark. The choke is working and the starter is turning over normal speed with a new battery. The weak Magnets could be a possible problem. I will have to put a meter on the stator and see what the reading is coming out.
Thanks for the help.
Rich

 

[wavrider]

Re: 115hp 1974 cranking issues

http://www.boatpartstore.com/page40.asp

Rich here is a chart for voltage measurements and resistance measurements.

those old cross flows require 300 rpm to make the voltage needed to have good spark to the coils.

fresh rebuild means good cpmpression and possible slower cranking speed

the newer carbs use a solenoid primer and inject fuel into the base of the carb behind the butterflys, this replaces the choke and quickens the start time with less cranking required for the vacuum to pull the fuel into the engine

I have a few of the v-4 cross flows and only one I updated the carbs to the solenoid primer type choke, this one starts easily once I shoot fuel into it for 10 seconds before cranking it the first time of the day.

Once you get it cranked the first time is it easy to start later in the day?
if it starts easily after the initial first start this is a hereditary trait of the older cross flows, only solution is to upgrade to newer model carbs with solenoid primer type chokes, this is if you are getting good spark

Use a spark tester and see if it jumps a 7/16" gap on all cylinders, if you get this 7/16" spark nice and blue then it is just the olf crossflow hard start syndrome.